For years, individual hydraulic automatic transmission manufacturers have specified proprietary automatic transmission fluids (ATF) for a variety of reasons. In the early years of ATF development, two manufacturers had significantly differing philosophies about automatic transmission clutch plate friction.
Ford used clutch plate materials and fluids that maximized static coefficients of friction and would result in quick, positive engagement when shifting gears. This eliminated slippage and its adverse affect on clutch plate life. General Motors, on the other hand, used different clutch plate frictional materials and fluids with friction modifiers designed to allow slippage by carefully controlling the dynamic coefficients of friction between clutch plates. Their clutch plate materials were less sensitive to wear caused by slippage.
Originally, Ford called their ATF Type F (later evolved to Mercon) and GM called their AFT spec Type B (later changed to Dexron). Type B and F fluids could be mixed together, but neither OEM would warranty transmissions if the incorrect fluids were utilized.
Caterpillar also got into this game when it introduced its Powershift transmission in off-highway applications. This began with the Cat Powershift TO-4 specification, which was designed to optimize the service life of their more rubber-like clutch discs.
Chrysler decided it needed to update its outdated ATF spec Type A due to automatic transmission failures. Their updated spec was called ATF +4. Pundits suggest that there could be as many as 100 different transmission fluid specs in the marketplace.
In recent years, we’ve seen the advent of continuously variable transmissions (CVT). CVTs have a completely different fluid appetite than traditional clutch pack and planetary gear set transmissions, so CVT OEMs created yet another set of specifications to deal with.
OEMs develop their AFT specs based on optimizing transmission service life in their proprietary transmission designs without regard to other makes. This is much the same as engine oil specifications for large natural gas engines.
Engineers at each OEM are specifying the best possible ATF for their products, but often their customers can’t get to a dealership for the proper OE fluid. I spent years in TMC’s S.14 Study Group listening to complaints from people having to stock too many different ATFs in their shops.
So, in the current United States ATF market, can a single ATF provide the same level of protection as each OEM’s proprietary product? The simple answer is no.
Any aftermarket ATF designed to meet multiple ATF fluid specs is a compromise. However, it is still better than using an incorrect fluid or running the transmission low on fluid.
I don’t see ATF specs coming together in the U.S. market in the near future, for the simple reason that each ATF manufacturer is highly competitive with its peers. Besides, OEM ATFs are priced at approximately 50% to 75% more than aftermarket ATFs, so most OEMs now realize than ATFs are a small but very profitable item.
The oil industry, on the other hand, would like to produce a minimum number of different ATFs to simplify logistics and storage issues. The Society of Automotive Engineers (SAE) Technical Committee 3 (TC-3) met earlier this year to discuss development of a performance based ATF fluid specification. This classification will be developed to enable the use of aftermarket fluids when OEM fluids aren’t readily available, if they can get the various OEMs to agree to a compromise fluid.
This is already happening overseas, where Japanese OEMs have developed a more universal ATF spec (JASO M315 1A) for aftermarket ATFs. Perhaps we can catch up to them in a few years.