Grease has been around for thousands of years. The name springs from a Latin word for fat, which ancients used to keep wagon wheels rolling. But while the technology has certainly improved, we still use grease.
Why? Think of grease as a sponge that holds oil and gradually releases it. That makes it useful where frequent relubrication is inconvenient. Also, grease can seal and protect components from moisture and contaminants. The principal virtue of grease – the fact that it stays put – is also a limitation. You can’t expect grease to perform the cooling and cleansing functions normally associated with oils. But, in the right applications, it’s the perfect solution.
What to use where
OEMs publish ratings a grease must meet to be acceptable for use on their vehicles at various lubrication points. However, these are minimum scores. Just because a grease meets them doesn’t necessarily mean it’s the best choice.
Stocking, and training technicians to use, several different kinds of grease, has its benefits. “There are advantages to using different greases in different vehicle areas,” says Dan Arcy, product marketing manager for Shell Lubricants. “For example, a tacky grease that won’t easily wash off a fifth wheel isn’t as good in high-speed applications, like U-joints.”
What about wheel bearings? Because they endure wide variations in speed and temperature, greases with good mechanical and high-temperature stability, designated NLGI GC, are desired. Normally, a smooth, lithium-based product works well, because it has good ‘slumpability,’ or ability to adequately penetrate rollers, races and cages.
Of course, most heavy-duty vehicles use an oil-filled hub to lubricate bearings and, according to the Technology & Maintenance Council, this is the preferred method, as it makes for somewhat cooler running temperatures.
However, some fleets that have had problems with leaky wheel seals have turned to mineral-based or synthetic semi-fluid grease for wheel bearings, since it won’t get past a damaged or improperly installed seal and contaminated brake linings.
Because of leakage, “our wheel seal maintenance costs were 10.5 cents per 100 miles for linehaul tractors, and 12 cents per 100 miles for trailers and dollies,” says Oren Summer, former director of maintenance of Carolina Freight Carriers and now president of FleetNet America. “That was two times our cost of clutch replacements, two and a half times transmission repair costs, two times electrical charging system repairs and two times starting system repair costs.
“We thought we might be able to solve the problem with a lubricant that wasn’t an oil or a grease – but something in between.” After extensive testing of a semi-fluid, synthetic grease, Summer noted positive results. “We started converting our trailers to the product,” he says, “and started spec’ing it on all new trailers and dollies. Our seal replacement costs went to 5.5 cents per 100 miles on linehaul tractor axles, and 3.9 cents per 100 miles on trailers and dollies, or about a 50 percent reduction.”
Summer adds, however, that, “Just because we were no longer replacing wheel seals between brake jobs, we didn’t want to assume that the wheel ends and brakes were ‘maintenance-free.’ So we continued inspection of the lube cavities and brake components, and had very good success.”
What’s best for the heavy stuff? Rubbing or sliding surfaces, such as metal bushings, ball joints, and other chassis and suspension components, require a grease with superior anti-wear and EP capability (NLGI designation LB). Lithium and aluminum-based greases, with an anti-wear agent like moly or graphite are well suited, since moly and graphite are friction modifiers consisting of tiny platelets that slide over each other like playing cards. They also adhere well to metal surfaces.
These greases are also good for fifth-wheel lubrication, but environmental concerns have led some to reduce the amount of grease used, since it eventually winds up on roadways, where it washes off and into water tables.
For that reason, fifth-wheel manufacturers have developed low- or no-lube products. Also, there are new, adhesive, non-grease-based lubes that eventually could be legislated into use.
For non-critical applications – linkages, door hinges and the like – almost any grease will do. These areas don’t see frequent or prolonged rubbing contact, so there’s no need for special additives. You can use chassis grease in these areas, but don’t use grease that’s only suited for hinges on chassis components.
One for all?
While there are advantages to using several, specialized greases for various vehicle areas, there are also sound reasons for keeping the number to a minimum. It’s a debate with no clear winner.
“We need to keep material data sheets on anything used in the shop,” says Lew Flowers, manager of vehicle maintenance for the U.S. Postal Service in Oklahoma City. “We have to manage everything, so it’s much easier to minimize vendors and products.”
“How am I going to get a mechanic to use this grease here and that grease there, when it’s enough of a challenge to get him to grease at all?” asks Bob Deal, president, Deal & Associates. “The simpler you can make it, the more likely it is to get done. And any grease applied is better than no grease.”
“We find that customers usually want one grease for 95 percent of their applications,” says Jeff Hollis, formulation quality manager for Castrol Heavy-Duty Lubricants. “So we try for a well-balanced grease across all properties – one that will pump when it’s cold, and stay put when it’s warm.”
“A good, lithium complex grease can be used almost anywhere,” says Lilo Hurtado, commercial vehicle application engineer for ExxonMobil. “Except wheel bearings, which need more high-temperature capability, and in automatic, onboard chassis lube systems, which require a thinner grease for cold pumpability.”
“We’ve tried to provide a bumper-to-bumper grease, except for wheel ends,” says Adrian D’Souza, ChevronTexaco’s manager of global grease technology. “It reduces complexity and reduces mistakes.”
Nicolas Samman, manager, grease product development, Petro Canada, disagrees and recommends at least three different greases. “Suspension components like spring shackles need a solid additive like graphite or moly, while a wheel bearing’s needs are much different. Fifth wheels need a grease that adheres, while auto-lube systems require good pumpability.
A ‘universal’ grease is a compromise,” he says.
“I recommend at least two or three different greases,” agrees Walt Silvera, 76 Lubricants product specialist. “Speeds, frictional characteristics and anti-wear requirements vary by vehicle component. Consolidation is a plus, but it may cost you some benefits elsewhere.”
The choice is yours
Grease manufacturers agree that modern, high-quality greases have been incrementally improved in the areas of: breakdown, corrosion and water resistance; tenacity; wear prevention; and life to regreasing. Service intervals, they say, have moved out, approaching those of engine oils.
So, after considering component application, how do you decide what grease(s) to offer your customers?
Some perform their own back-yard tests. Paul Manwiller, Air Products & Chemicals’ former director of maintenance, was notorious for attacking grease samples with his garden hose to observe resistance to wash-out. And, much to his wife’s chagrin, he tested for resistance to high-temperature breakdown in her oven.
“We’ve used the ‘hammer test,'” says Larry Jackson, owner, J&J Trucking and Packard Transport. “You put a good glob of grease on the face of a hammer, then give it a good whack against a solid metal surface. If there’s still grease on the hammer, it’s good stuff.”
Homegrown testing aside, grease manufacturers offer the following recommendations:
- Make sure the grease conforms to all minimum specs published by the vehicles’ manufacturers.
- Require your lube supplier to document that what you’re about to buy is compatible with with what you’re already using. Some greases don’t mix well with one another, and the result is usually excessive softening, leading to runoff and inadequate protection. If possible, try to find a grease with the same thickener you’re used to. In any event, a new grease should be pumped thoroughly through vehicle components to ensure that the old grease is purged as completely as possible.
- Don’t rely on appearance. Color means nothing, except that light-colored greases don’t stain as badly.
- Texture is limited as a measure of a grease’s quality. Contrary to popular myth, fibrous or tacky greases provide no advantage in lubricity over ones that are smooth, and they don’t pump or slump as well.
- Degree of oil separation has only limited value in judging a grease. Remember, grease is a sponge with oil in it. The sponge should gradually release oil, so a little separation in the container is normal.
- If your customers operate in a cold environment, low-temperature pumpability is an important consideration.
- Lithium complex greases are among the most versatile. These can be used almost anywhere on a vehicle, provided they contain some sort of anti-wear and EP ingredients.
- Finally, don’t buy on price alone. Ingredients like moly and graphite, in sufficient quantity to be effective, are expensive. And it’s a safe bet that you won’t get them if you don’t pay for them.
What’s in it?
Modern greases have three main components:
- Thickeners, often called soaps, make up the sponge part, and can be derived from calcium, lithium, sodium or other elements or compounds. Final properties, such as appearance, stability, pumpability and heat and water resistance depend largely on the type of thickener used;
- Oils, which can be petroleum-based, synthetic, or a blend, perform the primary lubricating function;
- Additives, which provide additional properties, such as corrosion-resistance, adhesiveness and extreme-pressure (EP) capability, may include sulfur, phosphorus, zinc, molybdenum disulfide (moly) and graphite.
Based on its ingredients, the finished product will display a number of measurable properties. There are standards for testing and rating each one, and vehicle applications where certain properties are more important than others.
