Match Fluids to Transmissions

When used in reference to transmissions, the term "genuine parts" conjures up images of gaskets, plates and bushings. But these days, its usage has spilled over into discussions about fluids, as well.

"We keep asking equipment to do more and more," says Jack Zakarian, consulting engineer at Chevron. "As a result, transmission fluids are becoming more of a 'genuine part'. They are more like gears and clutches where you can't take one manufacturer's parts and put them into another's transmission. Fluids have become part of the design of the transmission. Many builders consider them a design component."

That's why it's important to use the right fluid for your particular transmission. Manual truck transmissions require different fluids than automatics, and they each require different fluids than off-road, heavy-duty construction equipment with powershift or hydrostatic transmissions. You'll find fluid information for a particular transmission listed in the equipment operator's manual. Work with your oil supplier to match the specification to the product label of any fluids you're considering.

"Using the right fluid will improve the durability of a transmission," notes Dan Arcy, Shell, "whereas the wrong one can mask a problem and reduce the life of the transmission."

Arcy witnessed one such scenario at a car repair shop where shop technicians used tractor transmission fluid to "fix" a shifting problem in a passenger car. "Tractor transmission fluids have a high level of friction modifiers, which caused the clutch to slide," he says. "While those modifiers made the car easier to shift, the clutch ultimately wouldn't hold together and the life of the transmission was reduced."

When selecting a transmission fluid, also evaluate what you're trying to accomplish. If you want to take advantage of an extended warranty program or extended drain intervals, it likely requires the use of very specific fluids. In these situations, some contractors choose to use a synthetic fluid, indicates Mark Betner, heavy-duty product manager at Citgo. "Synthetics can offer superior low-temperature performance and long service life, and can better resist breakdown during sustained high-temperature operation. They have become very common in over-the-road truck transmissions and can offer benefits in light-duty transmissions, although they are not as common in off-road applications."

A growing list of options

When you factor in synthetics, as well as premium and traditional mineral-based fluids for each application, there are a host of options on the market. And the list is growing. "Everyone is getting highly specialized," says Zakarian. "There used to be one common automatic transmission fluid that would lubricate just about everything. Now there are at least six different types — and they aren't cross compatible.

"There are many different fluids because each transmission works differently," he continues. "There's a common misconception that there isn't much difference, but that isn't the case. If you want the best performance, you need to use the right fluid for the application. The bottom line is that any manufacturer who builds a transmission specifies its own particular fluid."

"Transmissions have been designed to work with a fluid that has certain characteristics, frictional requirements and seals that they're compatible with," adds Arcy. "If you use something that hasn't been tested for a particular transmission, you can shorten the life of components."

With an automatic transmission, the fluid has to provide just the right amount of friction on the clutch plates so they can separate quickly, yet hold together. "If you don't have the right fluid, you will notice poor shift quality and you get rapid wear of clutch plates or torque converter material," says Zakarian.