When a customer comes in complaining of trouble shifting or an odd noise when changing gears, your first reaction may be to question the health of the transmission. But because transmissions are sealed systems, it can be difficult to determine what’s really wrong. While wrenches might not be the most practical first step in the diagnostic process, analysis of the transmission lubricant can reveal information that can help accurately troubleshoot problems.
“Transmission lube analysis gives an early warning about potential problems before they result in expense and downtime,” says Richard Gapinski, driveline and ancillaries technical service manager, global lubricants technology, BP Lubricants USA.
Start by drawing a lubricant sample from the dipstick spout on an automatic transmission or from the side plug on a manual transmission.
“Make sure the transmission had been running and that the lubricant is mixed,” says Jack Zakarian, global manager, driveline technology, Chevron Corp. “You don’t want to go right to the bottom of the reservoir because if there’s any sludge or sediment that has settled out, you’ll pick up all that junk.”
After taking the sample, submit it to a qualified lab. It shouldn’t take long to receive results, which usually can be viewed electronically. The lab will run multiple tests on the sample. First, the tests check for additive elements, such as wear protection additives and detergents. Make sure the right amounts of these elements, based on the properties of the lubricant in its original state and the transmission OE recommendations, are present to ensure adequate protection.
Another test checks for wear metals. “One of the most critical elements to check for is iron,” says Zakarian. “All transmission gears have iron in them, so if you see iron in your oil, then you know that your transmission is wearing out. By looking at analyses over time, you also can tell by the amount of iron accumulating how quickly the transmission is wearing.” Other common wear metals found are copper, lead and aluminum.
Lube analysis also looks at viscosity and total acid number (TAN). Viscosity can indicate if the wrong product has been added for the transmission because the lube will be the wrong thickness. “It also tells you if it’s moved into a state of severe oxidation because the lubricant will thicken,” says Stede Granger, OEM technical services manager, Shell Lubricants.
The TAN test correlates with oxidation and can predict lubricant life.
Lube analysis may also uncover contaminants, such as coolant or silicon, which indicate dirt. Because the transmission is a closed system, the presence of any contaminants indicates a breach that must be addressed. Coolant leaks, in particular, can be catastrophic if not quickly detected and corrected.
Another benefit of transmission lube analysis is that it can be used to help customers extend their drain intervals, Gapinski says. With analysis, lubricant “is changed at exactly the right time, not too early or too late,” he says.
Recommended drain intervals vary by transmission make and lubricant type, but they typically are much longer than engine oil drain intervals because the transmission is a protected environment and doesn’t face the hostility of combustion. Still, many fleets and owner-operators want to extend drain intervals for transmission lube as well as for engine oil.
Higher operating temperatures associated with 2007-emissions compliance may cause heat deterioration in transmission lube. Because of these trends, establishing transmission lube analysis as part of your customer’s preventive maintenance routine may be more advisable than ever before.
What Exactly Is Oxidation?
When you take a bite out of an apple and leave it sitting on the counter, it turns brown. The discoloration you see is caused by oxidation, which literally means to combine with oxygen.
While you still can eat a mildly brown apple without suffering, oxidized oil wreaks havoc on an engine or a transmission. High temperatures, pressure and the presence of oxygen cause lubricants to oxidize, thus thickening. If oil thickens, it may not provide coverage to transmission gears, making them more susceptible to damage.
One Lubricant Doesn’t Fit All
Just as oil protects an engine’s components, transmission lubricant safeguards the transmission against part degradation, oxidation and wear. Automatic, manual and automated transmissions each require a different type of lubricant.
“The lubricant in an automatic transmission not only has to lubricate the gears and coat the clutches, but it also acts as a hydraulic oil,” says Stede Granger, OEM technical services manager, Shell Lubricants.
This means the oil has to maneuver through small passages in the transmission and cross various valves. Warm lubricant flows well, but in cold conditions, it does not move as efficiently, leaving gears unprotected. Because of this, transmission lube for automatics must be designed with strong low-temperature properties in mind.
“The viscosity difference between a lubricant for an automatic transmission and that of one for a manual transmission is very large,” says Jack Zakarian, global manager, driveline technology, Chevron Corp. “The friction properties of the lubricant are critical to making the clutches work correctly in an automatic transmission. It has to be smooth and can’t stick, slip or cause shudder, which are transmission vibrations. You need a lubricant that can pump through all the hydraulic circuits and control valves; it can’t be very heavy.”
A manual transmission does not put its lubricant through the same rigors. Here, the main concern is protecting the gears, which usually bear heavier loads. This is so important that many transmission builders consider the lubricant to be one of the design elements, Zakarian says. “It’s just like one of their factory parts,” he says. “The lubricant is a coherent part of the whole design.”
