Tips, techniques and features to enhance and maintain heavy-duty suspensions

When it comes to suspension systems, David McCleave knows that effective maintenance programs have a lot in common.

Grease guns are applied to zerk fittings; bushings are inspected regularly for cracks or tears; and, fasteners are tightened to the appropriate levels of torque.

The key components of a suspension maintenance program are the same regardless of the vehicle’s application. Fittings are greased, bushings are inspected and fasteners are tightened.

“The intervals can be very different from on-highway to vocational system applications,” says the director of aftermarket and technical services at Hendrickson, “but the key components to inspect are the same.”

Worn or failing suspension components can manifest themselves a number of ways, whether the challenges come in the form of extra vibrations or uneven tire wear.

“Incorrect ride height, worn longitudinal torque rod bushings or improper alignment can cause U-joint wear and vibration,” he says as an example.

“Also, improper rear suspension alignment can cause front-tire wear. This happens when a driver turns the steering wheel to compensate for the out-of-alignment suspension,” McCleave adds.

Ongoing inspections can keep issues like these from spiraling out of control.

While daily pre-trip inspections are an important tool in the search for damage, wear or loose components, annual inspections of a trailer suspension can offer the opportunity to dig a little deeper, says Michael Lynch, Meritor’s director of NAFTA customer service and product support.

This is when shops can check wiring and air systems for signs of abrasion; measure alignment; look for any loose, worn or missing components; check the torque on fasteners; and look for signs of oil leaks.

While daily pre-trip inspections are an important tool to finding suspension problems, an annual inspection gives the technician the opportunity to dig deeper and check wiring and air systems, look for loose components, check torque and measure alignment.

Abnormal tire wear can be one of the first signs of trouble, he adds. This issue may be linked to something as simple as improper tire pressure, but it also can indicate loose, worn or damaged parts.

Proper alignments will have a real impact on the life of the tires, says Brent Jones, SAF Holland’s national service manager – Canada. A one-hour realignment process could make a measureable difference in the life of treads that account for one of the largest operating expenses in any fleet.

In fact, SAF Holland’s SwingAlign system for highway trailers allows a realignment to be completed in less than 15 minutes, and without breaking the torque at the pivot connection. The key to the system is a set of teardrops connected to the pivot connection.

As a bolt is turned in the front part of the hanger, the beam is moved forward or backwards.

“Most trailer shops may consider alignments on a yearly basis,” Jones says. “This allows them to do alignments almost on a preventive maintenance basis.”

Proper torque for fasteners throughout the suspension system also will play a key role in ensuring that components of every sort move exactly as they should. In some cases, the fasteners themselves will make the difference. The head of a shear bolt actually will shear off once the proper torque values are reached, according to Hendrickson.

Unwanted issues such as cupped tires or damaged air springs can be traced to broken or bent shocks, McCleave adds. Shocks that show signs of outright fluid leaks or other physical damage will need to be replaced.

One of the most important tools used to inspect a shock will involve the simple touch of a technician’s hands. Once the equipment completes a 15-minute test drive, a working shock should feel warmer than the nearby frame.

“That’s because it’s doing exactly what it’s supposed to be doing,” Jones says. “It’s dampening or resisting movement.”

Proper torque for fasteners throughout the suspension system also will play a key role in ensuring that components of every sort move exactly as they should.

In some cases, the fasteners themselves will make the difference. The head of a shear bolt actually will shear off once the proper torque values are reached, McCleave explains.

The fasteners used on air bag pedestal mounts offer a good example of the need for proper torque.

“If you’ve got a loose pedestal, that air bag is going to be able to rock around on its mount, and then you end up cracking the pedestal or damaging an air bag,” Jones says.

“When you are reassembling a suspension it’s always important to re-torque the pivot connection with the unit adjusted to its proper ride height,” he continues.

“When you re-torque that pivot connection, it’s going to clamp down on the bushing area and potentially hold it in place so that when it’s relaxed or in its ride height position, the bushing itself is relaxed.”

This isn’t the only way that proper ride heights will play a role in suspension maintenance. A simple 2-in. change in the height of a fifth wheel could force an air bag to work outside its sweet spot, forcing the rubber to stretch more than it should and requiring more air pressure.

“Air bags have design limits, whether it’s fully compressed or fully extended, and there is a power curve that goes with that,” Jones says.

And the challenges are hardly limited to the air bags. “Ride height really affects a lot of components outside of the suspension itself.”

Granted, few flexible components are under more stress than rubber bushings. Inspections of these parts are largely limited to looking for signs of physical wear, McCleave says.

But original equipment manufacturers balk at the idea of shops experimenting with different bushing designs.

“The hardness of a bushing or a rubber material is really engineered into the product to allow enough give that the shock loads are absorbed, and the components have the ability to flex or twist in the manner they are designed,” Jones says.

A shop that opts to replace a rubber bushing with a rigid bushing in the search for a longer life actually may be transferring other stresses into welds, hangers or other components.

“There are certain components where the system requires a bushing to be bonded,” McCleave says, observing how a urethane bushing cannot bond to inner metal like its rubber counterpart.

Their focus on sticking to recommended components does not end there. Says Jones, “Suspensions are designed as a package. Each component complements the other, and if you take one of those components out and replace it with an external component outside the family of pieces it was designed for, you certainly can introduce problems.”

Of course, there still are plenty of cases where suspensions are being altered successfully in the aftermarket.

Unwanted issues such as cupped tires or damaged air springs can be traced to broken or bent shocks, Hendrickson says, referring to another factor to consider when inspecting suspension systems. Shocks that show signs of outright fluid leaks or other physical damage will need to be replaced.

Truckers who buy used linehaul tractors and convert the equipment for use on a farm, for example, would likely face more than their fair share of broken springs if everything was left untouched.

An option in this case can come in the form of rubber springs, which will reduce the flex in a pack of leaf springs, and offer some added roll stability, says Ed Sanders, national sales manager for Timbren.

These rubber additions also can help to level a truck when adding something like a 3,000-lb. wing on a snow plow.

As simple as the related installations may be, technicians installing the springs still need to maintain a 1-in. preload on a spring suspension and a ½-in. preload on an air suspension.

“In the heavy vehicle, because of the spring travel, we have to be engaged all the time, so it actually acts as a shock absorber as it works,” Sanders explains.

A few shims may be required to keep everything engaged. Individual suspension designs also can require some unique modifications of their own.

The rubber springs normally rest on a U-bolt pad, but sharp edges in some castings could lead to damage. Special brackets sometimes are needed to avoid this threat.

Regardless of what shops already have seen roll into their bays, technicians can expect to see more changes in the years to come. Engineers continue to fight the ongoing battle against unwanted suspension weight, using tools like Finite Element Analysis to identify areas of high stress, and finding other areas where metal can be removed.

Each manufacturer continues to unveil different approaches. Meritor’s RideSentry suspension, for example, uses structural “belly pans” to resist frame racking and increase the stability and strength of the frame.

SAF Holland introduced a cast suspension beam rather than the welded pieces of a fabricated beam. And Hendrickson’s integrated axle and suspension eliminated traditional U-bolt assemblies.

Who knows where this ride will take us next?

A properly installed and maintained wheel end will keep equipment rolling. Do you know how to make that a reality?

Let’s begin with a scary ending: Poorly installed and neglected wheel ends can lead to maintenance challenges ranging from uneven brake wear to catastrophic failures.

It doesn’t have to be that way. A focus on installation procedures, ongoing visual inspections and a few well-calculated adjustments can lead to much happier endings.

Visual inspections should begin by looking for obvious signs of leaks around the hubcap or seal, suggests Roger Maye, national service manager for ConMet. Some amount of seeping will be normal.

The worries are not limited to escaping oil, either. A lubricant with a milky color will likely be contaminated by unwanted moisture, which can exist if the wheels have been rolling through flooded areas. Some of the unwanted water may even be linked to pressure washers that were aimed at the hubcap or vent.

When inspecting wheel-end components, look for signs of uneven wear on the braking surface of the brake drum.

There also are other visible signs of trouble. While lubricants can be expected to darken with use, a dramatic shift in color or an accompanying burned smell can be a sign of excess heat. If you spot that, it is time to lift the vehicle to check for free and smooth wheel rotations and check for signs of excessive end play that would fall anywhere outside a range of .001 and .005 in.

But some issues may even be hiding in the depths of an oil bath. It’s why Maye likes to stick a magnet through the fill cap to see if it attracts any of the metallic particles that can be traced to peeling or spalling bearings, which can be caused by challenges such as an excessive pre-load.

The volume and condition of the lubricant should be inspected every year or 100,000 miles in a linehaul application and some situations will require more attention than that, he says.

“With use, the oil tends to dissipate, and you wind up with just the thickeners and the additives left and inadequate lubricant coverage on the bearings themselves.”

As important as the lubricant is, however, there are times when the bearings will require a close look of their own.

The bearing cone, which includes taper rollers and a metal or polymer cage, should be rotated slowly to look for signs of trouble like corrosion, metallic debris, pitting or metal flakes.

Only after the drum is inspected for hairline cracks, hot spots and other problems, should it be installed over the hub.

Any scoring can be a sign of dirt or grit, while a color that shifts from a straw brown to deep purple can be a sign of overheating caused by a lack of lubricant, a poor adjustment or excessive load.

“We’re seeing some issues of bearing cone race rotation in the industry right now with heavy-haul and wide-base tires with two-inch offsets. You want to look at the rear face of the mounting hardware and make sure it’s not damaged from cone race rotation,” Maye adds.

“If you see polishing on the (inside diameter) of the bearing bore, we recommend that the spacer be replaced.”

Bearings, meanwhile, should be checked for scoring that can be caused by excessive preload, spalling at the end of the roller that can be caused by issues like a lack of lubrication or excessive wear at the end of the roller that can be caused by a loose adjustment, SKF notes.

And in every application, both bearings and cones should be replaced at the first sign of any damage, says Leslie Kern, SKF’s product development manager – heavy-duty.

Even if one piece seems to be unscathed, it will have been damaged by contact with its mate.

The proper tools for removal and installation of wheel-end seals are critical to seal performance.

Installers also should note the first wave of pre-set hub assemblies heading into their shops do not use standard bearings, Kern adds.

“They look to be the same size, but (pre-set bearings are) especially tolerant, and also include a spacer,” she says.

Of course, every wheel assembly presents unique installation challenges. Unitized hubs, for example, can include unique locking systems, and torque values can vary from one manufacturer to the next. It’s one of the reasons why Maye and Kerns both stress the value of using Technology & Maintenance Council Recommended Practice 618.

But no matter which bearings are installed, these vital rolling components also should be kept in their packages until the last-possible minute. Used bearings should be stored in a clean solvent system equipped with a filter.

“Never put the bearings on the bottom of the container,” Kern says of the cleaning systems, referring to the area where sediment and debris tend to collect. And anyone who wants to apply a shot of compressed air also should be careful not to spin the rollers, since the air itself can carry some debris of its own.

Every piece needs to be handled with care. Tossing a bearing cage into a box filled with other hard components can lead to a deformed part.

“Treat the bearings like they’re precious,” she adds. “Once you clean it, you need to protect it until it gets inside the hub.”

When it comes to removing any unwanted rust and corrosion from a spindle, an emery cloth will be the tool of choice, but deeper grooves will need to be filled with a hardening gasket material and then buffed down with the emery cloth.

The seal’s landing area also will need to be clean, while chamfers should be clear of nicks or burrs.

“With aluminum hubs, you don’t want to use metal scrapers (which could damage the hub),” Kern stresses, suggesting a non-metallic scraper will be a better choice.

Actual installations also can benefit from a few tricks of the trade.

When replacing the cup in an aluminum hub, for example, Maye recommends welding a bead around the cup’s face.

“The bead will shrink the cup as it cools. The bearing cup will almost fall out of the hub assembly, and (the bead) keeps you from driving it out,” Maye says. “We have a higher interference fit between the cup and cone on an aluminum hub, and you actually can damage the bearing bore when removing the cup if you just drive it out cold with a punch and a hammer.

“But if you weld a bead around the face, and allow it to cool, you shrink the race and it comes out with very little effort, without potentially damaging the bearing core.”

A lesson in the applied physics of expansion and contraction also can help when re-installing the parts.

Simply chill a new cup in the freezer or with dry ice, and heat the hub in an oven at temperatures of 175°F to 210°F.

“You also can do that with things like boiling water or a steam cleaner,” Maye adds, referring to the heat source.

In contrast, a cast iron hub can be pressed in place at room temperature because there is less of an interference fit or chance to damage the hub.

Once assembled, a .002 in. feeler gauge can be used to ensure the cup is seated in place. Just check between the bottom of the cup and shoulder of the hub to verify that everything is completely seated.

The need to find a perfect fit even extends to the choice of seals, which should be perfectly matched to the wheel assembly. They also should be replaced rather than being re-installed since they can be damaged easily when removed.

As important as a new seal will be, however, it also needs to be installed with the manufacturer’s related tool — and that will never come in the form of a hammer or block of wood. Each tool is designed to apply pressure on a specific area of a particular seal.

When inspecting the many components in a wheel end, brake drums deserve a close look of their own, adds Johnathon Capps, product engineering manager for Webb Wheel Products.

“Look for even wear on the braking surface of the drum. You can use your finger tip and go around, and any sort of uneven wear is indicative either of mis-mount or potentially mis-machining,” he says.

Any sign of cracks through the braking wall will indicate it is time for a replacement, but fine hairline cracks are acceptable. In addition, any heat checks will form and wear away with use.

As rugged as they appear, however, there are limits to the amount of wear a brake drum can tolerate.

“It’s not very much for your standard brake drum,” Capps explains. “It’s typically 120 thousandths over the nominal braking surface diameter. That’s only 60 thousandths — or 1⁄16 in. — per radial side.”

A calibrated pin micrometer can be used to measure the largest diameter of the braking surface — including the grooves that can be caused by the buildup of debris between the drum surface and the lining.

Any sign of hot spots on the braking surface deserve some attention, too, since these locations will become harder than the rest of the braking surface, leading to unwanted vibrations and uneven wear.

“Any time you see any sort of ‘leopard spotting,’ it’s usually indicative of another problem, be it adjustment or drag. It also can potentially lead to cracks and failures,” Capps adds.

As similar as the brake drums may appear, installers also need to be aware of the differences that exist.

“A customer may get a tape measure and figure all the dimensions are the same except for the pilot may be a hundred thousandths off. That hundred thousandths is important. It needs to be the exact same,” he says.

Even storage procedures can make a difference. Rust can form on the surface of a brake drum that has been exposed to the elements, and this can affect the ability to reach proper torque values when it comes time to tighten everything.

Drums stored on their side also can warp, leading to vibrations or brake balance problems, and mounting flanges will crack if dropped from a pallet to the shop floor.

A little extra care obviously will lead to happier endings.

Part choices, maintenance and installation procedures all play important roles in hydraulic performance

When Nelson Jones says every hydraulic system should be well “STAMPED,” he isn’t talking about a label on the hose. The Gates Corporation fleet and hydraulic specialist simply uses the acronym to describe factors that affect performance.

Blistering occurs when a hose is incompatible with the fluids that flow through it.

No matter what system is involved, installers and technicians need to consider size, temperature, application, material, pressure, ends and delivery.

Forget any one of these factors and there can be consequences.

The choice of one hose over another offers a perfect example of the way size can affect a hydraulic system. Technicians who replace a hose with a version that has a smaller inside diameter could generate unwanted turbulence in the fluid, he notes. This can cause tubes to swell, cracks to form and pressures to drop.

Discussions about size are not limited to diameter, either. A length of hose in a hydraulic assembly can shorten by as much as four percent when it’s under pressure. “If it’s barely long enough to go from port to port, when it’s pressurized it will shrink a little bit and it actually will pull out of the coupling,” Jones explains.

Taut lengths may not matter as much when working with the lower pressures of a transmission cooler or hot oil line, but they will present challenges when working with the higher pressures that come with a power steering pump.

Refer to both internal and external factors when selecting a hose for a particular application.

“You always want to make sure there’s significant slack in the hose. You don’t want it sloppy, but you do want to build in sufficient slack to allow for changes to the pressurization,” he says.

When selecting a hose you will need to consider the demands of rising temperatures as well. The life of a hose can be slashed in half if the temperature reaches as little as 18°F above its maximum rating, Jones says. Every hose that looks shiny, glazed or blackened has likely been exposed to that unwanted heat.

For their part, suppliers have found several ways to address the higher heats generated by equipment such as the exhaust gas recirculation system found under the hood of a modern truck.

While traditional TWT (textile-wire-textile) hoses were created to handle temperatures as high as 212°F, options such as CPE (chlorinated polyethylene) were introduced to handle temperatures up to 300°F.

A hose with too small an inside diameter could generate unwanted turbulence in the fluid, which may cause the hose to crack.

Buyers also can watch for ratings such as SAE J1019, which proves a hose was able to stand up to a 750-hour bath in hot oil — and that can be a key consideration when installing a hot oil lube line.

There are times when the temperature-related support goes beyond the choice of material. The hoses that are mounted near hot components like a manifold or turbocharger may even need the added barrier of a heat guard to protect against constant temperatures that approach 500°F.

Of course, the threats are not limited to temperatures.

The inside of the hose will need to be compatible with fluids that flow through the openings, such as a phosphate-ester or a petroleum-based hydraulic fluid. Otherwise the hose can blister or even disintegrate and create debris that can plug different components found downstream.

Beyond that, the reinforcing layer provides the hose with its muscle, and the cover protects the reinforcing layer from the environment.

The key message here is that every option addresses a specific need.

A typical truck with a diesel engine can include more than 150 ft. of medium- and low-pressure hoses, Gates notes. The low-pressure hose that can handle 200 to 250 psi might work for fuel, oil or coolant lines.

In contrast, a power steering system, fuel filter or transmission coolant line might need a medium-pressure hose (or “flex line”) rated to handle up to 2,000 psi. For their part, high-pressure oil lines tend to include a wire braid, which can withstand higher temperatures.

Remember that hoses in an hydraulic assembly can shrink by as much as 4% when under pressure, so make sure the hose you install is long enough to account for the pressure-related shrinkage.

A hose with a braided reinforcement layer will include one or two plies of reinforcement, while a high-impulse hydraulic application might require four- or six-wire spiral reinforcement. Compare that to a suction return hose that would need to rely on a single thick strand of helical wire to keep the hose from collapsing.

Suction, return and pressure hoses are designed for their specific uses, notes Dick Henning, vice president of sales and marketing at BAB Steering Hydraulics Inc. Installing a double wire braid hose as a suction hose will create numerous problems.

A pressure hose (a double wire braid hose) will not fit properly on a suction hose barb (connection) and it cannot be sealed 360 degrees, regardless of the type of hose clamp that is used. In addition, the liner inside a pressure hose is held in place by pressure that is equal at all right angles throughout the system, while the liner in a suction hose is glued in place.

“We encourage people to think in terms of both internal and external factors,” says Jones, referring to hose choices.

“If it’s a pressure line, the fluid is pushing against the walls of the hose trying to get out. If it’s a suction application, the walls of the hose are trying to cave in because there’s a vacuum there. When you’re talking about heat, you want to think in terms of fluid temperature, but also you need to think in terms of ambient temperature. Both are factors today.”

Even though technicians will tend to replace a hose if they see any signs of leaking fluid, they may forget about the leaks in a suction hose that will draw air into the system, Henning says.

“When we say, ‘What is the first hose in the power steering system to leak?’ everybody responds, ‘Pressure.’ The reason they say that is because it’s a mentality we have. When we think of a leak, everybody thinks of fluid on the ground. But a suction hose leaks by ingesting air onto the system,” he adds.

Regardless of the hose that is used, installers also need to take care in the way every piece is routed and attached. Every option will have a recommended bend radius. And Jones notes how a seven-degree twist actually can damage the reinforcing layer and shorten the life of a hose by as much as 90 percent.

When choosing a hose, consider the demands of rising temperatures. Hose life can be cut in half if temperatures reach as little as 18°F above it maximum rating.

That’s why he always recommends using two wrenches, one to hold a back hex in place while tightening the hex at the very end of the fitting. The printing on the outer layer of the hose should remain straight and true with every turn of the wrench.

The focus on properly securing the hose can’t end there. When diving into dumpsters searching for damaged hoses — to use as examples in training sessions — Jones has found that every discarded assembly shows at least some signs of abrasion that could have been prevented.

Technicians who tie a pressure and return line together, for example, may not think about the way that pressure line will move as it encounters resistance. “People use a nylon sleeve or a poly wrap to bundle hoses together. That’s fine if they’re all pressure lines, but you don’t want to mix return lines in there,” he notes.

The life of a hose also can be shortened by the debris that flows along with the fluid. This is why a system’s filters require some care. “Filtration obviously is important and it can be overlooked,” Jones says.

When it comes to the power steering system, Henning suggests replacing the filter every time the engine is due for an oil change. In addition to trapping dirt, the 25 micron filters are needed to trap the metal removed from the shaft, he explains.

“Once air is in the system, and the air starts to implode, that implosion removes the hard chrome from around the seal surface,” Henning says.

It only takes 25 percent of the implosion’s energy to remove the hard chrome surface from the face of a shaft, and the remaining 75 percent is turned into heat.

Heat is what shrinks the wall thickness of a hose and makes the hose and seals hard and brittle. The more air is ingested, the more hose shrinkage, implosions and removal of the hard chrome surface.

Of course, there are limits to what a filter can accomplish. The debris inside a newly cut hose can do a lot of damage before it even touches the filter mounted by a reservoir. “If it’s a pressure line, that contamination is going to have one good trip down the system before the filter picks it up,” Jones says, referring to the installation work.

Rising pressures are increasing the potential for this damage. Twenty years ago, the typical operating pressures on a backhoe would approach 2,000 psi. Today’s pressures are double that, he adds. “That same level of contamination will cause a lot more damage in a lot shorter time.”

Much of this threat can be eliminated by clearing the newly cut hose of any debris, although the process involves more than a blast of air from a compressor.

Systems such as the Gates MegaClean projectile cleaning system combine the power of shop air, the nozzle for a specific size of hose, and a white foam plug or projectile that will run through the length of the hose to clear out the opening.

The projectile is fired through the hose in both directions before pieces are coupled in place, and sent through one more time after the pieces are connected.

Some makers of major components will void warranties unless the hoses are cleaned with a projectile, Jones adds.

The condition of the fluid is even more important in an era of smaller reservoirs. Power steering reservoirs, for example, once held a gallon of oil. Now they hold about one or two quarts of the fluid, Henning says. That is why he suggests it is important to keep an eye on the color of this liquid. Depending on the formula, unwanted heat will turn the fluid brown or black.

The choice of fluid also will differ from one system to the next. The correct fluid and type is determined by the manufacturer of the steering gear.

Ross does not like to see any synthetics; RH Sheppard systems will recommend synthetic fluids for specific gears. The challenge is that choices often are based on price. “Most people mix and match their fluids, which they shouldn’t,” Henning says, warning against the practice.

The attachments at every end of any hydraulic hose should reflect application-specific needs of their own. Screwed couplings will provide a tight fit with a coupling stem that is screwed into the hose, compressing the hose between the stem and the ferrule.

In contrast, low-pressure hoses can use connectors with stems and barbed ribs. Permanent couplings, meanwhile, are crimped into place.

Indeed, every connection in a system will require specific clamps. A suction hose, for example, needs a clamp that seals 360 degrees around the hose and barb.

A water type hose clamp does not offer a 360-degree seal. “The tang needs to be on the inside to compensate for the worm if you use that type of clamp,” Henning says.

These may all seem like minor considerations, but they can avoid some expensive problems down the road.

“In the steering system, particularly, it could take up to 18 months to see the effects of incorrectly installed or misadjusted gears, poor maintenance procedures, or the use of the wrong fluid, clamps or hoses,” Henning explains, referring to the way problems with a hydraulic system can manifest themselves.

A replaced gear that should last for five years may need to be pulled off the road in half that time. In cases where the original gears only lasted three years because of poor maintenance practices, the wrong hydraulic choices could further shorten the service life to 18 months.

It is simply one example of why it is always important to control the flow.

Make sure the air compressor is sized properly for the application. An overworked compressor can present a number of challenges.

Care for the Air

Eight ways to protect a tractor-trailer’s air supply

1. Remember Size Matters

The selection of every component in an air system should take into consideration exactly what will be powered, and how much air will be needed.

Like every other part on a truck, compressors and air dryers are sized for specific tasks. For example, a 13.5 CFM compressor may give a tandem trailer all the air it requires, but it will likely fall short if the tractor begins to haul a multi-axle Michigan combination, even if the drivetrain was strong enough to pull the load.

In fact, the compressor is only expected to build air up to 25 percent of the time. Duty cycles can be stretched to the limit by adding more air-powered accessories, making an unusual number of stops or leaving excessive leaks unaddressed.

If the compressor is overworked, a number of challenges can begin to emerge. The diameter and length of a discharge line, for example, might not be able to compensate for the warmer air coming from an overworked compressor. If that happens, oil will begin to pass through the system.

Meanwhile, the air dryer needs to be sized to handle the volume of air being pumped out by the compressor itself.

Aside from falling short in the battle against moisture and drops of oil, an overworked dryer will reach higher temperatures, and that can break down the related desiccant. These tiny particles have been known to work through air systems and clog the tiny orifices in ABS valves, jamming brakes into an on or off position.

2.  Seal Everything Tight

Any air that passes between the tractor and trailer will need to travel through the gladhands, so a secure seal plays an important role in delivering that air.

There should be little surprise that the gladhands’ seals wear out over time. In addition to the constant twisting that comes during coupling and uncoupling, any rubber will deteriorate over time.

Once these seals begin to degrade, drivers will begin to report hearing leaks when they disengage the parking brake or apply the service brakes. If the leaks continue, more air will be consumed, leading to an overworked compressor and air dryer.

The good news is drivers can replace worn seals with ease, as long as they are given a supply of spares. The seals even can be upgraded to polyurethane versions that tend to last longer than their rubber counterparts.

Of course, the gladhands are not the only potential source of leaks in these systems that involve an array of fittings, seals and connections.

There is a simple check to determine if there is a leak. After building up the air until the governor cuts out, allow the pressure to stabilize for a minute and then watch the air gauge for another couple of minutes. Then apply the service brakes and hold them in place for two minutes. If the gauge registers a drop of more than 4 psi plus 2 psi for each trailer, there is a leak that needs to be addressed.

3.  Keep It Dry

Any truck that operates in northern climes will rely on an air dryer to prevent moisture that can transform into ice. However, moisture can present problems in warmer environments as well, turning contaminants of all sorts into a muddy sludge that can slow the movement of valves.

It’s why these dryers deserve some ongoing attention of their own.

If water is freezing at the base of the air dryer itself, for example, the unit’s heater may not be receiving enough power. This situation often can be addressed by replacing a fuse or fixing anything that interferes with the heater’s circuit, such as a loose connection or a corroded wire splice.

But signs of moisture may not always indicate a problem. It can take several weeks for a retrofitted air dryer to catch up with the moisture in a system that has not been equipped with a dryer in the past. Some condensation also can be expected during trips where temperatures vary by more than 30º F.

4.  Keep It Clean

The potential contamination in an air system is not limited to moisture, either.

As small as the opening in a gladhand appears to be, it offers plenty of room for debris that can form a barrier between the tractor’s air supply and the trailer. Shops have seen these spaces filled with everything from grass and grit to beehives and cigarette butts.

The air still may be able to pass through this debris during a gentle brake application, but if the brakes are applied suddenly, the debris can compress and plug the air line. The result is a lack of brake power.

A few minor upgrades can make the difference. Inline filters and gladhand filters, for example, can be added to form a protective shield that traps particles as small as .0003 in.

Added protection also is available for times when the tractor and trailer are uncoupled. Options that will plug a disconnected gladhand, much like a pacifier that plugs a baby’s mouth, will help to ensure that unwanted debris like those cigarette butts are kept out of the system.

5.  Thaw With Care

Trailer technicians and drivers alike have been known to thaw frozen valves with liquid de-icers, but these fluids can lead to other problems. Options ranging from isopropyl alcohol to ethylene glycol antifreeze can cause the O-rings inside a brake valve to swell, and will break down the lubricants that protect internal pistons. Eventually, these issues can cause the valves to stick into place.

When de-icing fluids are used at all, only a small amount (such as 1/8 oz.) will be required, since it’s actually the resulting vapor that thaws the frozen components.

Of course, an alternative in the form of the warming touch of a torch’s flame can present a challenge of its own. The sudden and severe heat source can melt the rubber inside a valve.

It isn’t the only way that a torch can cause damage. A trailer technician who is welding brackets onto a trailer’s coupler plates may not stop to realize that, by heating the plates, he also is melting nearby air lines. When work like this is being completed, it is a good idea to place a piece of wood between the frame and the air line before applying the torch.

Consider what will be powered and how much air will be needed when selecting air system components.

6.  Check The Chambers

Given how close they hang to the road, there should be little surprise that brake chambers can be battered by debris, but that damage also can be more than skin deep. Dents may be a sign of internal issues such as compromised seals, which can cause brakes to drag.

The choice of a replacement chambers can make a lasting difference to the system’s performance. As similar as the designs may appear, different brands can generate wide variations in stopping forces. This will make it important to install the same design at both ends of an axle.

Keep in mind that value-priced models may present some challenges of their own. Corrosive de-icing compounds have been known to travel through the vents in some designs, and some chambers simply are clamped together rather than welded shut, potentially exposing technicians to the explosive po wer of a compressed spring.

7. Be aware of the weakest links

Kinked lines, poorly installed fittings, faulty valves or damaged chambers all can be causes of sluggish performance.

Filters are designed to prevent debris from plugging air lines.

Indeed, no matter what individual components might promise, the overall system will only be as strong as its weakest link. A 3/8-in. hose rated at 1,000 psi, for example, will only be as strong as the 500 psi coupling that is used for a connection.

Different manufacturers also accept different tolerances in the products they make, meaning the fits of any connections can vary from one brand to the next.

8.  Don’t vary the valves

As similar as valves might seem — right down to the position of the ports for the air lines — there can be big differences in the internal components. Some models will relay air immediately, while others remain closed until a specific crack pressure is achieved. The valves installed in an individual system are designed to feed air to each wheel end at the same time.

A decision to force a different valve into place can throw that balance out the window, causing aggressive brake components to wear out more quickly, or actually affecting how the trailer will track when coming to a stop.

But if a shop is careful to install the right components, everyone will have a chance to breathe easy.

•Sources: Bendix, Haldex, Meritor WABCO, Phillips, Truck Watch Services

Fully operational

Proper PTO installation provides a Class 8 truck with a valuable resource.

Used primarily to power an external powered attachment, a PTO is able to provide power anywhere under a truck and works through the drive line.

Although most PTOs are installed during original assembly, a PTO added in the aftermarket can be installed in 30 minutes or less. But like most components, a PTO requires more than a quick installation to remain effective. Preventive maintenance and proper service also are keys to maximizing the effectiveness of an external PTO.

An external power take-off is powered through a mating gear inside the drive line of a truck transmission. A PTO can be installed to the transmission and linked to the mating gear in 30 minutes.

The first step in the acquisition of a PTO comes in the truck-buying process. According to Jeff King, marketing manager at Parker Chelsea, not every heavy-duty truck is built with a transmission that features a PTO accessible gear.

Most are, but King says it’s not entirely uncommon for a truck with an automatic transmission to not include PTO capabilities.

“It’s not always a standard option for a transmission,” he says. “If you’re buying a truck with a manual transmission, it is going to come with the PTO drive. With an automatic, it’s not always standard to have one.”

However, some automatic transmissions come with a PTO option. At Allison Transmission, all products in the company’s Rugged Duty Series are specifically designed for PTO use.

Lou Gilbert, North American director of marketing for Allison, says the Rugged Duty Series is built with multiple PTO apertures and is compatible with any PTO product line.

The addition of a PTO drive gear to an automatic transmission can cost up to $6,000, King says. PTO installation is much cheaper and easier with a compatible transmission.

Most PTOs used in heavy-duty trucks are installed to power a hydraulic pump located under the truck’s main frame.

The pump is used to disperse hydraulic fluid through the cylinder, and cool heated fluid that has circulated through the motor.

In Class 8 trucks, the pump is activated by engaging the PTO when the transmission is in neutral.

Installing a PTO to power the pump takes time and skill. The first step to installing a PTO is draining the oil from the transmission and removing the PTO cover plate, King says.

The PTO will be installed to the mating gear located below the plate. Once the plate has been removed, King says it’s important to remove all gasket debris where the PTO will be installed and check the location and quality of the gear inside the transmission.

Next, the technician should set the backlash units between the mating gear of the transmission and the PTO. Parker Chelsea recommends a backlash of 6,000 to 12,000 units for its PTOs.

“You can set the backlash by adding or subtracting gaskets,” King says. “For us, we equate a 10,000 gasket as 6,000 backlash (units) plus or minus, and a 20,000 gasket is 12,000 (units) plus or minus.”

A loose PTO sounds like a jar of marbles, King says, while a PTO installed too tightly will create a whining noise. Both situations can damage the mating gear and the PTO. King says a simple dial indicator used to measure the backlash when the PTO is installed can prevent both problems.

After the backlash has been measured, it’s time to attach the PTO to the transmission housing. PTOs attach to different transmissions in different locations, but all PTOs need to be mounted directly onto the transmission frame to access the mating gear.

Once installed, the PTO is held in place by a fasteners connected to the transmission’s housing.

Depending on the PTO’s use, a drive line can be added to the completed PTO once installed to provide power anywhere under the truck. But the addition of a drive line means the addition of extra brackets under the truck to house the PTO, and added safety precautions to avoid PTO-related accidents.

Because of this, King says it’s become common to use the PTO to power a device close to or directly next to the PTO and transmission. As a matter of fact, that’s becoming the standard with hydraulic pumps.

“A lot of people are beginning to mount the pump directly to the PTO,” King says. “It eliminates that need for a drive line and allows you to install both at the same time.”

King also recommends performing basic maintenance on the PTO once it’s been installed. He says greasing the PTO shaft before use is an excellent start, as is checking to make sure the PTO’s electronic controls function correctly from the cab.

The PTO can only be engaged by using controls inside the truck, so proper wiring and connectivity from the PTO to the cab is paramount.

After the PTO is operational, it’s important to set a maintenance schedule. Parker Chelsea provides service maintenance handbooks for its PTOs, and King says common checkups and diagnostic exams by qualified technicians eliminate a lot of potential problems.

If regularly serviced, a properly installed PTO should run for quite some time.

“I always tell anyone installing a PTO to tie into the preventive maintenance schedule of their transmission,” King says. “The two work together, you should think of them that way.”

For an Allison Transmission, preventive maintenance includes fluid and filter changes. Gilbert says those changes aren’t affected by an attached PTO, and are recommended at 75,000 miles for the filter and 300,000 miles for the fluid.

Since Allison doesn’t provide PTO products, Gilbert recommends following the PTO manufacturer’s service manual for additional maintenance requirements.

King says regular service inspections every three months and visual inspections should keep a PTO running; and he says it doesn’t take a genius to know what to look for when checking a PTO.

A tight or loose PTO has its own distinctive sound, and a PTO can leak just like any other part.

“People do inspections on their trucks every day when they look at the engine, the tires, the trailer, things like that,” King says. “They look everywhere around the truck, so we just tell them to make sure they also look under the truck. You don’t have to crawl under it, but you can look to see how things are. It’s just like if you see an oil leak. If you look at the PTO and you think you see a problem, you can fix it before you get out on the road.

“No one wants to break down when they’re out on the road,” he says. With proper PTO service and installation, you don’t have to.

Tips for troubleshooting (and avoiding) HVAC problems

If filters are not cleaned, restrictions can develop

Frank Burrow admits that Red Dot Corporation was mystified when a customer called to report a four-speed blower fan that only worked at a single speed. Every piece of information seemed to suggest everything should work as designed.

Then one member of the team asked whether the cab filter had been replaced.

“Filter?” the customer replied.

The air began to flow as it should once a new filter was in place, and future problems were avoided in the process. “If cab filters are not cleaned on a regular basis, they can cause all kinds of problems,” explains Burrow, Red Dot’s manager of warranty and product support. “This is an area where we can blow up blower motors because of the restriction.”

The situation that was addressed by this manufacturer also demonstrates the importance of asking as many questions as possible when trying to troubleshoot HVAC problems.

During HVAC system service, be careful not to introduce contaminants into the system.

Many of the issues with an HVAC system will only appear when a certain number of factors are combined, so shops need to take the time to record exactly what happened at the time of a failure. If a driver reports that the system stopped cooling, when exactly did it stop? What did the driver do when that happened? Has it happened before? Does he still feel air coming through the vents? Is there any cooling at all?

Equipped with the right details, a shop often will be able to uncover problems that would otherwise go unnoticed.

The potential power issues that might shorten the life of a compressor’s clutch offer a perfect example of some of the problems that could be hiding.

“Clutches on the compressor require a very good ground and a good power feed. As long as we keep the voltage there, we’ve got a clutch that’s going to last as long as the guy owns that piece of equipment,” Burrow says. If there is not enough power, however, the clutch hub will slip against the face of the pulley, generating friction and temperatures that soar above 1,000º F. “It quickly can melt the clutch bearing seal as well as the epoxy compound that seals the coil.”

When working as designed, the receiver-dryer should be warm to the touch.

An initial look may suggest that the clutch is receiving the 11.5 volts of power needed to generate an electromagnetic field, engage the clutch pulley and allow the refrigerant to flow. But it still will be wise to mimic the situations that exist when the system is running outside the shop. “If you’ve got all the lights off and you sit there and take a reading, it may look wonderful. It may look like 12 volts. This guy turns everything on and all of a sudden you’re at 10 volts. Guess what that clutch is doing? It’s slipping because it’s an electromagnet. It depends on that current flow to pull it tight,” he says.

Any attempts to grade the power supply also should reflect the actual installation of the clutch. “If it’s a single wire, the clutch sees its ground on the compressor. Don’t run your ground to the chassis. Don’t run your ground to the motor. Run your ground to the compressor. Duplicate what the clutch is seeing,” Burrow adds.

Power issues, such as an improper ground or poor power feed, can shorten the life of the compressor clutch.

As important as the questions for drivers may be, a well-trained technician also can determine many issues with nothing more than a close look or a careful touch of his own. If a clutch is slipping, for example, the front of the hub also will begin to discolor and the rubber caps can melt. This normally can be seen with the help of a mirror.

The careful looks should not be limited to the clutch, either. Many problems with an HVAC system’s connectors often will be identified by their related oil stains or dirt, while the pink, white or gray dot on a receiver-dryer’s moisture indicator will identify the presence of acid or moisture.

“The second (most important) set of tools you have is your hands,” Burrow says. “If certain components have a lot of ice on them and they’re not supposed to, you’ve got a problem.” The temperature of a receiver-dryer offers a perfect example of the challenges that can be spotted. When it is working as designed, a receiver-dryer will be warm to the touch. Any sign of ice will indicate a restriction in the system.

Make sure the system’s filter is cleaned and properly positioned.

Of course, shops also need to make sure they are not introducing new challenges of their own during any repairs.

A system that is uncapped for too long will open the door for contaminants, and any connections that are put in place need to be sealed properly before the equipment is returned to the road.

As similar as they may appear, there are even differences between one O-ring and the next. Red Dot likes to use HMBR O-rings that will not swell. They also are lubricated just before being installed. “Use virgin product, oil it up, make sure you seat it all the way onto the fitting,” Burrow suggests.

A well-trained technician can find many problems by closely inspecting the system or merely by touching certain components.

The required torque will vary depending on the fitting, he adds. A Number 6 O-ring fitting will need 11 to 15 ft-lbs of torque, while a Number 8 will require 15 to 20 ft-lbs, a Number 10 will need 21 to 27 ft-lbs and a Number 12 will need 28 to 30 ft-lbs. “We want to make sure they’re not overtorqued — and especially not undertorqued,” he says

One final step also can help to identify potential future problems with any connections. Some anti-tamper tape or even the stroke of a felt pen across two mating parts will make it easier to spot a fitting that has vibrated apart.

And the care of the system’s filters will provide some ongoing protection — as long as everything is clean and properly positioned.

The arrows on a new (or cleaned) filter should be aligned with the desired flow of air. If the filter includes an aluminum mesh that offers some shape and substance, the mesh side should be downstream since it will hold the media in place and keep disintegrating pieces from being sucked into the motor.

To help troubleshoot an HVAC system, make sure to find out exactly what happened at the time of the failure.

But when cleaning a pleated paper filter, remember to vacuum from the side where the air normally would enter. “You don’t want to suck dirt through the filter. You want to suck it out the way it came in,” Burrow says. Meanwhile, filters made with open-celled foam can be washed with soapy water.

A number of filter designs also will help enhance the overall performance of the system. Charcoal-impregnated filters, for example, can help trap odors, while HEPA filters can trap the tiny particles that would otherwise affect people with allergies or asthma.

As important as different filters can be, however, shops also need to be careful about the compounds they introduce into the systems.

The shelves of most parts stores are lined with one-pound cans of 134a refrigerant, but maintenance teams should be wary about those that are combined with oil and sealant, Burrow suggests. “You don’t know what oil is in there, and every compressor manufacturer today generally uses its own unique blend of oil.” While most compressors use polyalkylene glycol refrigerant oil (better known as PAG oil), others use synthetic ester oil. If the wrong formula is added, the compressor’s warranty can be voided.

Burrow is equally concerned about cans that include sealants. “Sealants look for small openings to plug,” he says. “The system works because it has change-of-state points, and one of those points is at the expansion valve — and it is a very small opening.” The refrigerant will not be able to reach the compressor if the expansion valve is clogged. An exact volume of the material is important, too.

Most compressors are pre-charged with between five and 10 ounces of oil, but there will be a difference from one model to the next. And there is no need to add any oil when installing a new pre-charged compressor. In fact, if too much oil is added, the lubricant actually can form a thermal barrier inside the components.

“Five percent of the volume of gas they’re bringing in will have oil in it,” Burrows says. “If we start increasing that ratio, at some point we’ve got liquid coming into a piston-driven compressor, which generally doesn’t do well.” That’s when reed valves will begin to bend, altering the suction and discharge pressures along the way. Eventually that heat will be transferred to bearings and cause a clutch failure.

Shops obviously need to take every possible step to protect against an HVAC attack.

With scheduled cleanings and a little care, a diesel particulate filter should enjoy a long service life.

Diesel Particulate Filters (DPFs) hardly enjoy an easy ride. The can-shaped addition to exhaust systems — needed to meet 2007 emission standards — faces an ongoing attack in the form of high temperatures, pressures, vibrations and corrosive chemicals. In the face of all that, they are expected to capture soot, reduce everything to a fine ash and hold the remains until it is time for a cleaning.

But decisions and steps in the shop can help determine whether the filter will make it from one scheduled cleaning to the next.

The choice of engine oil certainly can make a difference. “Most OEs have designed the aftertreatment systems for exclusive use with CJ-4 oil,” notes Matthew Leustek, a Caterpillar on-highway engine core technology and systems engineer, referring to the low-ash formulas that were made possible with the widespread introduction of Ultra Low Sulfur Diesel (ULSD).

“Not using CJ-4 will lead to measurably worse fuel economy over time due to higher ash accumulation rates, potentially lead to DPF failures, potentially lead to low-power complaints [because of elevated back pressure], and may lead to the inability to effectively ‘ash service’ the DPF in extreme cases.” It will be difficult to measure the change in fuel economy from month to month, but a trend will emerge over a year, he says.

Granted, a typical build-up of ash should be largely unnoticed by drivers, notes Ed Saxman, product marketing manager for Volvo Trucks North America. “In reality, both the inlet air filter and the DPF are large enough that, with proper maintenance, there is not a significant difference between a new filter and a dirty filter.”

A DPF usually will arrive in a shop when it is time to address its increasing load of ash. That is when teams will need to decide whether to clean the equipment themselves, or participate in an exchange program offered by an OEM.

While the cleaning process largely uses a controlled shot of air, it involves more than reaching for the hose attached to the shop compressor.

The ash doesn’t build up evenly across the entire filter, explains Drew Taylor, national sales director and minority owner of FSX, which provides equipment used by shops including Navistar, Kenworth and Peterbilt dealerships. A cleaner that fails to account for the difference will leave behind deeper channels of ash that eventually will transform into dense “pencils” that actually can change the thermal characteristics of the filter.

“When the onboard active regeneration system hits that DPF with a whole bunch of heat, that heat is going to clash with the cool zones,” he says. The result will be an unwanted crack and a costly replacement. At the very least, the added ash will limit the filter’s surface area and reduce the amount of time between cleanings.

In the FSX system, the cleaning takes place in a sealed cabinet where a series of moving “air knives” blast air into both ends of the filter core, breaking up any ash and sending it to a central SootSucker dust collector. Once the cleaning process in this TrapBlaster is complete, an FSX TrapTester is used to measure the thickness of any ash under 750 cfm of pressure, which is roughly what would be generated by a 13L engine running at a high idle of 3,500 or 4,000 rpm.

The photo on the left shows a diesel particulate filter prior to cleaning. The one of the right shows what a cleaned DPF should look like.

If the cleaned component fails to meet the “green tag” range associated with the identified filter, the DPF is placed into a kiln known as the TrapBurner, where it will be baked at temperatures of up to 1,112ºF for up to 12 hours. By then, the filter should be free of any soot and ready for a final cleaning in the TrapBlaster.

While most states will allow the resulting ash to be disposed in a landfill, Taylor expects a growing number of jurisdictions to follow California’s lead, where the debris is classified as a low-level hazardous waste.

Systems like these have yet to find a home in every shop, but Taylor suggests that the machines will offer a return on investment after just one cleaning per day. The set-up also is relatively simple.

His company’s equipment can be matched to any source of three-phase power, while the TrapBlaster itself will draw air from a compressor that delivers at least 120 cfm of air at 100 psi, similar to what would be delivered by a typical 30-hp rotary screw compressor.

If the shop needs to use more of the air downstream, the cleaner’s requirements can be cut in half by using one air knife at a time. That simply doubles the traditional 30-minute cleaning process.

Still, some shops are deciding to leave the cleaning to others, with Volvo, Mack and Detroit Diesel collecting cores, cleaning the filters and refining the inspection process. Even when it is loaded with ash, a 40-pound filter will weigh about the same as the day it was installed, Saxman says, questioning the accuracy of other inspection methods.

The difference is so slight that Volvo uses a scale which reaches all the way down into the bedrock, just to ensure it can accurately measure subtle weight changes in terms of grams or tenths of a gram. That way, there is no question about whether any ash remains.

The actual removal or replacement of the DPF itself is a relatively simple process that takes less than half an hour, using nothing more than a simple shop jack. In the case of a Volvo truck, a fairing around the fuel tank hinges out and off, while the filter itself is held in place with band clamps and connectors.

“Place the dirty one into the protective shipping box and return it to the dealer for another. It’s that simple,” Saxman says. “The whole process doesn’t require a service bay.” Anyone in the shop who can change brake linings will have the skills needed for the task.

Granted, there is a need for some care. Installers need to properly align any

O-rings when putting a new one in place, and be careful not to drop the filter. “The last thing anyone needs is a worthless piece of ugly ceramic art,” observes David Mc­Kenna, Mack’s director – powertrain sales and marketing.

Ongoing preventive maintenance is largely limited to inspecting the inlet’s flexible piping or the tubing that feeds the delta pressure sensors. Cracks or loose clamps around the inlet flex pipe could sacrifice some of the passive heat needed to oxidize any of the soot, he warns.

And if the DPF itself is cracked or partially melted, technician will notice a black coating on the surface behind the filter.

“If you see smoke coming out of a truck with a DPF, it’s got a crack in the DPF,” Saxman adds, noting how the damage could be caused by collisions or stressed V bands. “That’s really a giveaway that it’s broken.”

But there are other potential sources of trouble. The DPF could be fouled by oil that escapes through the turbocharger, or a bad seventh injector that leaks unwanted fuel into the exhaust stream, McKenna says.

The injector itself is designed to add fuel to the catalyst to force an “active” regeneration of any soot when sensors determine that the “passive” heat in the exhaust system has not completed the job. (Volvo and Mack actually have eliminated the active regenerations in 2010 engine designs, and rely entirely on the passive approach.)

One of the most common causes of DPF failures even occurs in the shops themselves, when technicians fail to follow all the necessary steps while using a service tool to force an active regeneration, he says.

A filter might appear to be clogged even though the issue is really linked to pressure sensors that are plugged with carbon. If these small tubes are not inspected and cleared, the regeneration process will lead to extreme heats which actually could crack the device.

“We have a diagnostic tree that you really have to follow. If you start cutting off branches to where you want to go, you will miss items,” McKenna says.

In cases where the DPF is clogged prematurely with heavy levels of soot, the challenge usually is traced to a driver who has used an available switch to stop an active regeneration. (The switches are put in place so drivers can halt the process if they are in an area where an idling engine would lead to unwanted noise, or when the added heat actually could present a hazard.)

Another cause could come in the form of a clogged seventh injector, or heat that is lost through a crack between the turbo outlet and the DPF’s inlet. If the latter situation occurs, drivers likely will report smelling the fuel for short periods of time. If they report excessive exhaust noise during a regeneration cycle, the problem likely will be traced to something like a loose clamp or cracked flex pipe, McKenna says.

Given the high cost of the filters, Saxman suggests that the next generation of used truck buyers will be focusing on the ongoing care that a DPF receives. They will want to know that the device still has many miles of service ahead of it.

It is a particular interest that can be expected to increase over time.

Tire pressure monitors, inflation systems could make tire gauges a thing of the past.

The days of the humble tire gauge probably have been numbered for awhile. Systems that could automatically detect tire pressures were on the market as early as the 1980s, when Imperial Clevite unveiled its Tire Tele. As of 2007, pressure monitors were even mandated on all new vehicles with a gross vehicle weight rating below 10,000 pounds.

But while this equipment is a legislated reality on the family SUV – thanks in no small part to the power of the Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act – the pressure monitors or automatic inflation systems for heavy-duty trucks and trailers need to be promoted on their own merits.

“It could be years before anything is mandated,” admits Al Cohn, director of new market development and engineering support for Pressure Systems Inc., which offers the Meritor Tire Inflation System.

Even when the Federal Motor Carrier Safety Administration (FMCSA) unveils its latest research findings about the technology this February, the equipment’s use is expected to remain voluntary. TireStamp, whose TireVigil system transmits tire data to drivers and fleet managers alike, reports that an approach similar to SmartWay is more likely. The Environmental Protection Agency uses that program to promote a long list of fuel-saving options.

“Each individual fleet has to look at its own bottom line,” suggests Richard Van Dyke, vice president of Fleet Specialties, which offers the Tire Sentry monitoring system. And when the potential return on investment is considered, the benefits of today’s tire pressure monitoring systems or automatic tire inflation systems can become pretty clear.

Tire pressure monitoring systems, such as the TireStat system from Mobile Awareness, typically include in-cab displays that relay tire condition to drivers. Because of the distance between the trailer tires and the cab, TireStat uses a transceiver on the trailer to broadcast the signal. The second photo shows how the TireStat pressure sensor, which is shown in both photos, is installed on the tire. Mobile Awareness uses flow-through valve stems so that they don’t have to be removed when topping off a low tire.

One of the promised returns comes in the form of fuel savings. Recent research by the Standards Testing Laboratory in Massillon, Ohio found that when pressure is allowed to drop as low as 70 psi, a truck tire’s rolling resistance increases an average of 12 percent. In the real world of an on-highway tractor-trailer, the added effort to roll the tire equates to a 2.3 percent drop in fuel economy, researchers concluded.

Now consider how widespread the issue actually is. According to FMCSA’s Office of Bus and Truck Standards, about 7 pecent of all tires are underinflated by 20 psi or more, and only 44 percent are within 5 psi of their target pressures.

“Diesel fuel is going to average $3 per gallon, and is projected next year to be up over $3.25,” notes Brandon Stotsenburg, vice president of sales and marketing for Mobile Awareness, which offers TireStat monitors. “People are going to start seeing the return on investment of the systems going up.”

The fuel saving potential is cited throughout the latest marketing material for most of these products. Meritor Tire Inflation Systems’ thru-T and delivery hoses even have been colored a bright green to highlight the environmental benefits. But proper pressures are not just needed to save fuel. They can help to extend the life of tires as well.

The added flex in a poorly inflated tire will generate the heat that shortens the life of a casing, limiting the number of retreads or leading to an outright failure. The FMCSA went as far in one study as to suggest that improper tire inflation accounts for about one road call per tractor-trailer each year.

Tires also are expected to face some added scrutiny under the new federal carrier rating system known as CSA 2010, Cohn adds. Trucks and trailers with flat tires are penalized with eight points. Underinflated tires carry three.

There is no denying that a properly calibrated tire gauge also can be used to monitor a tire — and it is the cheapest option of all — but anyone who has used one of the simple tools will understand why inflation issues often are hidden until the damage is done.

It can take 30 minutes to press a tire gauge onto 18 valve stems, so many truckers “monitor” their tire condition with nothing more scientific than a kick to the sidewalls. The traditional tire gauges are not always that accurate, either. “A lot of tire gauges very quickly get out of spec’,” says Stotsenburg. Even a calibrated model can be off by several psi after being dropped on a shop floor.

The systems which address tire pressure can largely be divided into two separate categories. A tire pressure monitoring system (TPMS) offers a warning about

low tire pressure, while an automatic tire inflation system (ATIS) actually delivers air to offset any leaks. The warnings from electronic monitors can be delivered in the form of a light on the sensor itself, an RF signal that activates a monitor in the cab, or even cell signals which can send data as far away as a fleet office.

This technology also has proven to be quite accurate. After studying several options, the FMCSA concluded in a 2009 report that the equipment offered false low-pressure readings 6 percent of the time and missed the problems a mere 2 percent of the time.

“The more frequent issue was ‘no reads’ resulting from missing sensors, failed sensors or sensors in the wrong wheel locations,” researchers said.

In fact, one of the biggest challenges came in the form of keeping track of the valve-mounted sensors themselves. One of the conclusions was that users should train everyone who will come into contact with the systems, limiting the chance for sensors to be discarded, misplaced or simply mounted on the wrong wheel.

When attached to the wrong wheel, some sensors could fail to point drivers to a specific wheel end. “RF signals are floating around in the open market, so each sensor has a unique ID code,” Stotsenburg explains. That ensures a monitor will not measure the low-pressure warning from another trailer parked nearby. Then again, this leaves room for improvement.

“They have to be able to do a drop and hook process that is easy, so when you hook up the seven-way [J560 connector], you have that communication transfer,” he says, adding that his company plans to address the challenge with a 2011 product launch.

Most systems alert drivers and fleets to tire pressure-related problems, but the Meritor Tire Inflation System from Pressure Systems Inc. (PSI-MTIS) also inflates underinflated tires by tapping into the trailer air tank. To highlight the environmental benefits of its system, PSI-MTIS uses green parts throughout the system.

There are other variations in the systems. Some products, for example, allow the sensors to be programmed for different pressures, which could be useful for those fleets who want to set different thresholds for steer and drive axles.

An added component needed on combination vehicles often comes in the form of transceivers or antennas, which can relay signals from a trailer’s wheels into the monitor mounted inside a truck. There is simply a lot of distance and metal to cover between the rear axle and the dashboard. TireStat, for example, mounts a transceiver on each monitored trailer; the Tire Sentry system includes an antenna under the cab; and Stemco’s BatRF boosts the power of its messages with a 2.4 GHz signal.

TireStamp pulls information from a sensor mounted inside the tire, and uses telematics to feed the data everywhere from the dashboard to a fleet office. Email alerts are generated for problems such as a low tire or rising temperatures, but the company also offers a portal with charts and graphs which can be analyzed to support tire programs across the organization.

As the examples show, there are even differences in the way sensors are mounted in place. Some are strapped inside the tire, while others simply screw directly onto the valve stem or onto the end of an extender that reaches the stem on the inner tire of a dual wheel assembly. Mobile Awareness sensors take the latter approach a step further with a flow-through valve stem, so they do not need to be removed when topping up a low tire.

An anti-seize compound on the tire valve’s thread will be particularly important to protect against any seizing or galling when the sensors are exposed to highways that are covered in de-icing compounds, Van Dyke adds of the threaded options.

There is no question that commercial wheel ends present a punishing environment for any of the products. In the FMCSA tests, for example, some sensors mounted to wheel housings became brittle, cracked and failed in the face of excessive heat. (That challenge was addressed by mounting an isolating pad on the bottom of the sensor, where it contacted the rim.)

As electronic products, the valve stem designs also require batteries to stay alive. Many sensors that do not allow battery changes extend the life of the units with an “intermittent” approach which measures the tire pressure at a pre-set interval, and only when the wheels are turning. When the battery dies after several years of use, the entire sensor needs to be replaced. In contrast, the Tire Sentry system sends out a continuous signal, and its simple watch battery can be replaced in the field.

Tire Sentry’s electronic valve caps incorporate pressure sensors and microchip transmitters. The 2-inch display on the Tire Sentry system not only detects a low pressure situation but also identifies which of the 18 wheels on a combination vehicle is experiencing that condition, making it easier for the driver or mechanic to address the situation.

Automatic tire inflation systems take the monitoring a step further and actually offset any losses in the air pressure.In the case of the Meritor Tire Inflation System, the controls come in the form of a control box and regulator mounted onto a cross member. They feed air into the hollow trailer axle, and then out through the spindle into a rotary union. A couple of hoses deliver the air to the tire.

An added feature in the form of a ThermALERT sensor will even warn about problems that could lead to tire fires. A thermal screw, officially known as a eutectic insert, is mounted at the end of the spindle. If the heat begins to rise because of a problem such as a dry bearing, the insert’s material will melt, and the 100 psi of air will begin to shoot through the 1/8-inch hole. “It will make this loud, obnoxious banshee noise,” Cohn says of the warning.

Most of the Meritor systems are sold as original equipment, but one in every five still is installed in the aftermarket. While there is no question that they take more time to install than the sensors on a valve stem, technicians can equip a typical van trailer in a mere four hours, Cohn says. Specialized tools are limited to a press plug driver, and one of the few installation tips involves blowing out the axle to remove any debris before adding the connections.

Cohn also suggests watching over related torque values. The rotary union, for example, is attached with a mere 50 inch-pounds of torque. A tighter twist will lead to an unwanted leak.

There are differences in the systems to consider as well. The Dana Tire Inflation and Monitor System (TIMS), for example, feeds its air through hoses that run through the axle, rather than the tube itself.

But technology of every sort continues to feed the idea that traditional tire gauge may be a tool of days gone by. It will certainly help in the cases when the gauges are not used at all. n

Most engines deserve a second life. The quality of that life will depend on the rebuilding process.

By John G. Smith, Contributing Editor

Fans of the 1970s TV show “The Six Million Dollar Man” will remember how astronaut Steve Austin was introduced during the opening credits: “A man barely alive. Gentlemen, we can rebuild him. We have the technology.”

The same can be said about a modern diesel engine. The technology is available to rebuild equipment that has been reduced to little more than a hulking mass of metal – and at a price considerably lower than the $6 million bill for a bionic superhero.

But the work may not be as frequent as some experienced technicians rememberM. “We’re now talking about B-50s at 1.2 million miles on these engines. When we started in this game it wasn’t unusual to have a B-50 of 400,000 miles,” observes Jay Wagner, MAHLE Clevite heavy-duty product specialist, referring to the point at which one in every two engines would require an overhaul.

Brian Gordon, a regional manager at IPD, offers an observation that is less optimistic. “The days of a million-mile engine have come and gone,” he counters, largely blaming exhaust gas recirculation (EGR) systems for introducing more contaminants into engine crankcases, shortening the life of rings, cylinder liners, piston ring grooves and more. He suggests a typical B-50 life is more likely to fall somewhere between 600,000 and 700,000 miles depending on the engine model.

Ironically, that shorter life could actually improve the case for an overhaul. These engines will be sitting in younger trucks, so there will still be plenty of life in other components.

The decision to rebuild an engine must make economic sense. Factors to include are the remaining life of other components on the truck and which components on the engine need to be remanufactured or replaced.

Of course, the ultimate need for an overhaul will be dictated by more than the mileage on the odometer. Oil analysis programs can identify spikes in the volumes of unwanted wear metals and other contaminants.

“If metal particles are present, this could point to failure of the rod, main bearings or cam bearings,” explains Mack Engine Product Manager Danny Long. “An oil analysis will also indicate if there is a high concentration of fuel or antifreeze mixed with the oil. If so, the piston rings could be failing or excessive wear to the piston liners has occurred. Antifreeze contamination can cause premature wear to the bearings as well. The next step is to run a compression test on each cylinder. Low compression can be caused by worn liners and piston rings, or even worn valves.”

Those who operate the equipment can identify other factors such as engine knocks or misses, smoke from the exhaust, increased fuel consumption, higher blow-by rates, and an overall drop in engine performance, notes Brad Everett, Caterpillar’s on-highway senior product support analyst. “A more general indicator would be mileage, engine hours or fuel consumed as measured by the engine ECM [electronic control module].”

The vehicle’s application will dictate how important one factor will be over the next, he explains. An engine exposed to high idle times would likely be evaluated based on engine hours or the gallons of burned fuel instead of the mileage recorded on an odometer.

What needs replacement will vary, but generally the water pump should be replaced along with the rod, main and cam bearings, pistons, piston rings and liners, oil pump, thermostat, seals and gaskets.

A test on a dynamometer might offer the most telling information of all. The Caterpillar representative refers to a test on a chassis dyno which measures the engine’s fuelling rate, horsepower, torque and blow-by. “There are established specs for all of these and if any of these are out of spec, there may be something wrong inside the engine,” he says.

Ultimately, the most important factor in the decision to rebuild an engine may come down to a matter of economics. Virtually anything could be rebuilt. If the lower bore on a cylinder block is in terrible condition, for example, it can be cut out and enhanced with metal inserts; if the crankshaft journals and connecting rod journals show signs of excessive wear, it may be time to remove the cylinder block.

But there is an array of other components which can add to the complexity and cost of the job. An electronic fuel injector can cost $3,000 to $4,000, and there might be six of those to replace.

Many engines will also include two turbos in the turbocharger, each of which can potentially fail, Gordon notes.

Rick Cape, Mack’s remanufactured technical product manager, refers to the way the water pump should be replaced with the injector cups and even the injectors – along with the rod, main and cam bearings, pistons, piston rings and liners, oil pump, thermostat, seals and gaskets that should be part of any rebuild.

Wagner, however, looks at another price-related issue that should increase the interest in rebuilds. The latest generation of engines created to meet the emissions regulations of the U.S. Environmental Protection Agency are more expensive than the generation that came before. That makes them worth saving.

Advanced manufacturing processes have eliminated much of the technician prep work for replacement components. The shop environment where the rebuild is taking place also needs to be as clean and free of contaminants as possible. Even microscopic debris can wreak havoc on engine performance.

But the most affordable rebuilds will always tend to be those that are planned through the regular analysis of the oil, and before a catastrophic failure. If a rod breaks while the vehicle is cruising down the highway at a high rate of speed, the damage always will be more severe. “That piece of metal swinging around can almost cut the block in half,” says Wagner.

“If you wait until a major failure, you risk having to replace additional parts as a result of contingent damage, driving up the overhaul cost significantly,” Everett agrees. “If you can, it’s better to plan ahead, budget for an overhaul at the appropriate time, and take advantage of the built-in second life of the engine.”

Repair shops should certainly play a key role in that guidance.

The work may even be more than a matter of just fixing the engine. Thanks to different updates, a shop can take steps to enhance the engines that need to be rebuilt.

“If there’s been any design changes or improvements to a specific component, the servicing dealer technician can make sure the latest and greatest for the customer’s specific engine model is incorporated into the overhaul. Additionally, there are sometimes updates to engine ECM software that may enhance the overall performance of the engine,” Everett says.

“Depending on the age of the engine, a piston redesign may have occurred,” Long adds. “This is typically done to reduce NOx emissions or strengthen the piston for quality reasons. An ECM reprogram may also be needed in conjunction with the piston replacement or as a standalone upgrade. Higher compression [meaning more power], less oil consumption, improved fuel economy and lower emissions will be the ultimate gain.”

The end result is better. Stronger. Like the Six Million Dollar Man.

But there are limits. A shop that decides to boost a 350 hp engine up to 450 hp by spending nothing more than another 20 minutes with the ECM may be heading into dangerous territory. It is possible, Wagner admits, but the changes can have a “cascading” effect on the other drivetrain components that were never built to handle the added stress.

“Trying to figure out all the repercussions of trying to change the horsepower is sometimes a worrisome thing,” he says. “It’s like a light bulb. The hotter it burns, the less time it burns.”

REQUIRED PARTS

The list of components needed for a rebuild will seem pretty familiar from one engine rebuild to the next. There will be new pistons, rings, liners and seals in addition to the cylinder head, but the job can involve much more than that. An in-frame overhaul can still involve machining and cutting counter bores into shape, along with the cylinder packs, injectors, and water pump. Meanwhile, an out-of-frame overhaul will involve sending the block and related components to a machine shop.

It is important to consider the nature of any problems that led to the decision to rebuild the engine when deciding on the steps and parts which will be required, Wagner says. If an engine was running poorly for no apparent reason, a shop may be able to identify an issue such as a lost cam lobe. An overheating engine may lead to questions about the cooling system. And an intake manifold full of oil should lead a technician to investigate the condition of the turbocharger.

The decision to replace parts such as aftercoolers or water pumps will often be dictated by a schedule set by the manufacturer, Wagner adds.

Different nameplates introduce needs of their own, leading sources like the Engine Builders Association (AERA) to publish regular bulletins about rebuilding procedures.

“Sometimes there’s a fairly good list of them on any engines,” Wagner says. “They really are the ones calling out the anomalies.”

Newer, emissions-compliant engines cost considerably more than their predecessors. This higher purchase price may make owners more likely to rebuild in the future.

Material choices will always play an important role as well. For example, a 14.5:1 piston is simply not an alternative for the 15.5:1 design used in the original engine. “I’m amazed how many pistons they’ll make to fit the same size bore,” Wagner notes. The wrong choices are even more likely when the parts are chosen visually. “You’ve got to know what size your crank is,” he adds. “If you put one in too tight the engine won’t turn.”

Main bearing caps also need to be installed in the proper order. “A rod cap is exclusive to that rod,” he explains, stressing the fact that the parts are not interchangeable. “If you have six rods and put No. 5 cap on No. 6, you’re going to have a rod failure…you have to put it in the right direction, too.” Arrows will also indicate the front of a piston in many cases. “If you’re not paying attention and put the pistons in backwards and the valve hits… it does tend to make a lot of noise!”

Cape, meanwhile, notes how a crankshaft may need to be turned or polished to remove the scratches made by failing bearings. “These parts need to be inspected during the parts cleaning process to identify worn parts,” he says. “Sometimes a technician can simply inspect the part and tell if it is worn beyond its service life; sometimes a technician must make measurements using precision tools.”

But Gordon also warns that there are different interpretations of “new” components, and that could affect the ultimate life of the rebuilt engine. Cylinder packs may simply include used and reconditioned parts. “You can’t expect new life out of used parts,” he insists. “It works the same thing with cylinder heads and water pumps.”

CLEAN CONDITIONS

Another source of future failures may have nothing to do with the choice of parts at all. Few shops can match the sterile environment of an assembly line, and every bit of contamination threatens the life of a rebuilt engine.

“Cleanliness is the No. 1 thing all the time,” Wagner says, noting how debris can be displaced every time a part is moved. When working on an in-frame overhaul, he stresses the need to seal off the fuel system and close the lines using plastic caps. When machining a cylinder, the adjacent cylinders will also need to be sealed with caps of their own.

Gordon offers advice of a similar nature: sealing injectors into plastic bags, closing openings such as fuel lines with tape, and sealing the turbo’s exposed oil galleys. The bases of oil filters, coolant filters and fuel filters should also be covered and protected. In fact, he recommends leaving the old filters in place until they’re ready to be replaced.

Dirt even seems to be attracted to the oil holes in connecting rod journals. If left behind, it is likely to jam itself into a bearing, thanks in part to changes that have included a thinner, harder coating. “They reduced the amount of that babbitt material to 30 to 40 hours. It doesn’t have the ability to tolerate contaminants like it used to,” he says.

Some contaminants are unknowingly introduced in the name of cleaner parts. The same solvent that cleans one surface, for example, can wash contaminants into the connection rod journals. Meanwhile, the material used in bead blasting can jam itself into plenty of crevices, and it will only be knocked free by the oil in a running engine.

“That’s going to be embedded in all the bearings,” Wagner says.

His solution? Don’t bead blast. Other cleaning media, such as walnut shells, will be a better option. “You can do anything you want,” he continues, “but only as long as you’re careful enough to clean everything out.”

It is about more than avoiding debris. A Scotch Brite scouring pad can peel the sealing bead off the top of a liner; an abrasive wheel used to remove a gasket can ruin the surface of the spacer plate underneath; and glass or steel shot will actually wreak havoc with the smooth surface of a ring even though it appears to leave a mirror-like appearance. “You roughen it to the point where it makes it hard for the ring to rotate,” Gordon observes.

Wagner notes how the thinking extends to the newest parts. Some technicians think new liners need to be re-honed, even though today’s refined manufacturing processes have eliminated the need for some of the preparation. The liners are already “plateau honed,” which means that any microscopic peaks are already knocked off the surface. “The honing stone they use to get the right cross hatch is very precise,” he adds.

Even the addition of some extra lubricant can cause some trouble. Few of the seals are made simply of rubber, and some of them do not respond well to a technician’s grease.

“Most gaskets are designed to put on with no sealant,” Gordon observes. “If you think putting a bunch of silicone on it is helping the situation, you could be making it worse.”

The gasket sealer can also squeeze into an engine and plug an oil cooler. “Look at what’s in the end of the oil cooler and a lot of times it will be silicone,” he notes.

His solution? “Liquid dish soap will almost never create a problem.”

QUALITY CONTROL

A few extra tests and inspections will also avoid trouble as the renewed engine continues its journey.

Engines with overhead cams, for example, have introduced the need to inspect the cam shaft and cam followers. “Cam bearings are now considered normal in an in-frame overhaul,” Gordon says, noting how such inspections had been considered an option unless a customer was willing to have a radiator removed. “You just left them alone, crossed your fingers and hoped they were fine.”

Then again, with an ISX Cummins, the radiator actually needs to be pulled out to access the head bolts. The access is already granted.

Ultimately, the surface of the cam shaft and cam follower should be inspected for signs of pitting and fracturing – the spalling that will lead to hairline cracks where cam followers run on pins. “There are specs on how much movement can occur on the cam follower roller itself,” he adds.

Even though today’s injectors are more durable than their predecessors, it can also be a good idea to test their performance before reinstalling existing versions in the engine. And turbochargers deserve a look of their own. “There’s a thrust bearing in there,” Gordon explains. “You can check for end thrust to make sure you have proper end-to-end movement.” If the compressor wheel touches the housing, “bad things happen.”

The final test on a dynamometer may include the most important inspection of all.

“If something is going to go wrong it’s going to go wrong on the dyno,” Wagner notes. If the engine is tested when outside the frame rails, it will also be easier to identify the source of something like a coolant leak.

Since the material on the face of any of the new rings is harder than ever, the final break-in period for the renewed engine will be an important final step, Gordon adds. It may be possible to seat the components by coupling the truck to a trailer and dragging the brakes, but a dyno ensures that the work has been done correctly.

It is further proof that a shop can rebuild it…if it has the right technology. n

A careful investigation is the key to bringing vibrations under control.

The hunt for causes of unwanted vehicle vibrations can seem like a game of hide and seek, and a costly version of the game at that. Many technicians attack the issues by replacing one questionable part after the next in the misstaken hope of finding the source.

Sometimes they are lucky. Often they are not. And customers can remain all shook up in the process.

This was certainly the case for the first 300 trucks that Eaton hooked up to its Driveline Vibration Analyzers (DVA) about five years ago. Technicians had been baffled by the shaking vehicles, which had each averaged about $9,300 in related repairs. But equipped with the modern diagnostic tool, teams identified most of the issues within a day, leading to fixes that averaged little more than $900, plus the identified repair.

“It takes down all the guesswork,” says Eaton Product Service Manager Lon Miller, referring to the value of the diagnostic tool. “I’ve never seen it be wrong.”

And the technology keeps getting better as electronic vibration analyzers continue to evolve.

The attachments that now fit under the driver’s seat give the graph-producing tools an accurate idea of what a driver literally feels in the seat of his pants, measuring individual frequencies that can be matched to specific components from wheel ends to drivelines. One speed channel is simply screwed into the engine’s flywheel housing while a similar attachment sits at the rear of the transmission, working much like a speedometer that tracks a spinning tone wheel.

Anything that focuses the troubleshooting efforts will be a welcome alternative to throwing new parts on a truck until the problem disappears. “We’ve had people install a new engine in the truck and still have the same vibration complaint,” notes Zack Ellison, director of customer technical support at Cummins.

“The OEMs do a much better job today than they did 10 years ago,” he adds, referring to the improvements in the use of mounts and the way these individual components dampen noise, vibration and harshness (NVH). But vibration-related troubleshooting efforts may need to be more refined than ever now that drivers have come to expect more of a car-like ride.

As valuable as diagnostic tools like an electronic vibration analyzer can be, troubleshooting efforts can still benefit from a few pointed questions to the driver, especially in shops where the tools are not available.

“When does it do it? When doesn’t it do it?” asks Charles Allen, director of global customer service at ArvinMeritor, referring to the valuable details about vibration complaints. “Try to be that specific because that can help guide you.”

For example, a vibration that only occurs when the engine is not in gear will eliminate driveline issues, but driveline vibrations will likely emerge at a specific speed and become harsher as the speed increases. In contrast, a vibration that occurs at a specific speed and then disappears when the truck begins to travel more quickly might be traced to problems with a tire or clutch.

If a technician is able to join the customer on a test drive, there should be no question about where the vibration occurs. The added advantage of this clear understanding is that there will be a way for the teams in a shop to ensure that a repair has actually “shut off” an unwanted shake or rattle. That is the ultimate goal.

WHERE IS THE TROUBLE?

Unwanted vibrations can be traced to a host of issues, such as an imbalanced driveline or wheels, overhung transmission or the pulses from the engine itself (after all, the combustion process involves an ongoing series of controlled explosions). Or, a damaged clutch may be unable to dampen the vibrations that emerge whenever an engine hits 1,400 rpm.

Yet one of the most common causes will emerge when someone readjusts an air-ride suspension in the name of a smoother ride. That simple act may soften the ride down the highway, but it can also change the angle of the driveline. And incorrect operating angles can lead to a pile of vibration induced troubles including failed transmission gears, synchronizers, differentials, axles, transmissions, pumps or blowers, and the gears, seals and shafts of a PTO.

The operating angles can be measured with an electronic protractor and fed into the software from the component supplier to determine the best possible settings. In general, operating angles should be set at no more than six degrees, while three degrees is best, says Karl Mayer, ArvinMeritor’s director of product line management – drivelines.

“In the case of inter-axle shaft, and really any system where you have two universal joints, you want to make sure the two angles cancel each other out.” This requires the angles to be within one degree of each other. Left uncorrected, the vehicle could face problems with transmission synchronizer pins, or damage to U-joints – often the No. 4 U-joint found at the output of the forward rear axle on a typical 6×4 tractor.

“Realizing the sensitivity of vibrations and how drivelines may or may not impact that, we’ve actually tightened the specifications of the amount of imbalance we’ll allow in the driveshaft,” Mayer adds. “It’s a much, much tighter specification and we realize that’s going to help.”

Never overlook the easy fixes.

Of course, the physical condition of the parts can make a difference as well. A dented driveshaft tube or a missing weight might throw a driveshaft off balance. Even if this issue is not noticed by the driver, it could still lead to vibration-related damage.

And those who are removing the component have to be careful to reassemble everything in phase. The yokes will normally be in line, but there are situations where an OEM will ask for special phasing, which can be identified by the combination of a straight weld seam but a turned yoke.

A few simple marks will ensure that everything is lined up as it should be, Allen adds.

“If the vehicle OEM has chosen to phase the driveline a certain way…you don’t want to just rely on, ‘I think it goes this way.’”

But the driveshaft may be blamed for vibrations more often than it should. It may be easy to replace, and the part is relatively inexpensive compared to the price of a transmission or rear axle, but it isn’t always the culprit. “You’re always going to be able to find some amount of imbalance,” Allen explains. Even if shops invest the time to “super balance” the component, there may simply be other factors that play a bigger role in an unwanted vibration.

“By far, the majority of vibration issues [over 90 percent] have to do with wheel ends,” Daimler Trucks North America suggests. The solutions to these issues will involve maintaining balance weights, or rebalancing tire and wheel assemblies whenever replacement parts are installed.

“How well they are centered [runout] is also something to pay attention to when mounting new tires,” company representatives adds. “Using or spec’ing centrifuge [balanced] drums helps. Most shops have a way to measure runout so these components are centered within specification.”

Additionally, customers are pushing their tires longer than ever, and many are not balancing or aligning the wheels when installing the new rubber, Miller says. For those customers who do this as a cost-cutting measure, the long-term expense could be hefty. “You’re setting yourself up for a problem,” says Miller.

UNDER-HOOD CAUSES

Other vibration issues can be traced to the mounts and isolators that are designed specifically to protect trucks, components and drivers from the unwanted shakes.

“Even though these look like simple blocks of rubber, a lot of thought, design and testing goes into a good isolating isolator,” adds Daimler Trucks North America personnel.

It would be difficult to underestimate how important these isolators are. Look at the engine alone. Every combustion event will lead to some torque spikes. That can lead to the vibrations which can wear out main bearings, main journals and crankshafts. Luckily, newer engines have been refined to address these challenges.

“When we build an engine there are certain things we can control in the manufacturing process, and we balance the piston, rod bearing, crankshaft and rotating parts, and we work on how we time or phase the air compression into the engine,” says Cummins’ Ellison. Pistons are machined within a few grams of each other. Even the connecting rods are more precise. “They don’t let the [manufacturing] dies run as long as they once did, so the parts come out very, very close.”

Drivelines unfairly get blamed for vibration-related complaints.

But even when all that is in place, drivers still can begin to report the issues like shaking mirrors that might emerge at low idle speed. That usually can be controlled with engine mounts, as long as the components are working as they should.

A twisted engine mount that allows metal-on-metal contact can present an issue of its own. This “short circuit” can be caused if the frame rails are misaligned, Ellison says. Then the engine’s vibrations will be amplified as they travel into the frame rail.

Installers simply need to be careful about the replacement mounts that they choose. Softer engine mounts may offer a better feel for the driver, but there is a trade-off in terms of shorter component life, notes Mike Bastuk, Cummins’ director of OEM service. The ultimate choice will need to strike a balance between reducing vibration when the engine idles at 600 or 650 rpm and being firm enough to handle the stresses of peak torque.

“The slower the idle speed, the softer the mounts have to be to reduce that natural frequency,” Ellison says. The trade-off is that the life of the mount is sacrificed.

Of course, any of the mounts also will deteriorate over time, and that will happen through the flexing and twisting that comes with day-to-day operation.

Switching drivers can make a vibration magically disappear.

Signs of deteriorating rubber will be easy to see, Ellison says. “You’ll see in some cases where it’s actually melted the rubber…you can see cracks.” But it isn’t always a matter of replacing these parts. Bastuk has seen cases when vibrations have been solved by simply loosening the existing mounts and retightening everything in place, eliminating the dreaded metal-on-metal contact.

It is not the only example of a solution that can be surprisingly simple. A fastener or bracket might simply need to be retightened to hold a component or accessory in place, eliminating a rattle that drivers perceive as a vibration. Recommended torques are also particularly important in the fight against unwanted vibration. “The endplay of the bearing or setting of the bearing may require that nut to be tightened to a certain torque,” Allen says.

Never overlook the easier solutions. Bastuk refers to one situation when a cab began to shake as the truck idled at 600 rpm. He simply decided to reset the speed at 700 rpm and the problem disappeared. “In a lot of cases, if the complaint is at idle, you dial it up 50 rpm and see if that fixes it,” Ellison agrees.

Fleets have even been known to address the problem by assigning a different driver to the cab. Vibrations can be a matter of perception, and the problem identified by one driver might magically “disappear” with the next.

Miller also stresses the importance of a simple preventive maintenance step that can prevent many vibration issues before they occur.

“The best thing you can do is just grease,” says Miller. Even “maintenance-free” drivelines will dry out, and the grease applied to any U-joint should also purge at all four trunions.

There is simply no reason to be shaken by a vibration-related complaint when you’re taking steps like these. n