Automatic Transmission Fluid and How It Works
A Slightly Confusing History of Automatic Transmission Fluid
Today's automatic transmissions are nothing short of mechanical marvels. Originally designed as two-speed devices, transmissions developed by manufacturers today are rapidly moving to 6 and 7-speeds to improve driveability and performance, as well as economy. Today's transmissions are incredibly sophisticated, requiring in many cases their own specific fluid formulations. Gone are the days when ATF was ATF, and nearly all cars ran on the same stuff. Selecting the proper quality of ATF is not as easy as it once was. In the past, ATF was basically called Type A and was used in the primitive transmissions developed in the 1940s. By the 1950s it came in two types: ATF Types A and F. GM used A and Ford used F, but cars would run pretty well on either. However, as transmissions became more advanced, automobile manufacturers introduced fluids specifically designed for their transmissions.
ATF is the most complex of all lubricating fluids. Not only does it have to reduce friction to prevent wear like all lubricants, but it also has to allow a certain level of friction so the transmission's internal clutch materials can engage. Since most OEMs use proprietary frictional materials, virtually every ATF is OEM-specific. In some cases, they are transmission-specific. In addition, ATF's must be compatible with all transmission components, operate at both low and high temperature extremes, and maintain constant performance for extended periods.
To accomplish these complex tasks, ATF typically contains the following components:
Sludge & varnish control
Planetary gear, bushing, thrust washer protection
Modify clutch plate and band friction
Prevent corrosion and rust
Seal swell agent
Prevent loss of fluid via seals
Reduce rate of change of viscosity
Pour Point Depressant
Improve low temperature fluidity
Automatic Tranmission Fluid Identification
As you can see, ATF has to do a lot of things for a very long period of time, so quality and formulation play a big part in today's transmission fluid chemistry. The good news, however, is that our older transmissions will work beautifully with the new fluids, provided we install the correct one. Below is a list of fluids and their applications.
Here are the most commonly specified ATF's:
This is a specification for General Motors vehicles, but many foreign manufactures specify a DEXRON approved ATF as well. DEXRON-III can be used in transmissions that call for DEXRON-IIE or DEXRON-II.
Most Ford vehicles manufactured between 1980 and 1999 specify a MERCON ATF. ATFs that meet DEXRON-III requirements usually meet the MERCON requirements as well.
Beginning with the 1997 model year, Ford introduced a higher performance level ATF with the MERCON V specification. Many Ford automatic transmissions from 1999 on will require a MERCON V fluid. The most notable exceptions are the E40D, 4R100, and CD4E transmissions, which still specify regular MERCON ATF.
Type F is specifically designed for all pre-1977 Ford vehicles and some makes between 1977 and 1981. Effective March 1997, Ford discontinued administration of approvals for Type F fluids. However, there are still many vehicles on the road that use Type F. Type F and MERCON fluids are not interchangeable.
DaimlerChrysler has had their own ATF specifications for many years, but as of 1997, Chrysler owners' manuals no longer list DEXRON as an acceptable replacement. ATF+3 is a readily available mineral oil-based ATF that is suitable in any application calling for ATF PLUS(r) , ATF+2(r) , or a Type 7176(r) fluid. Vehicles manufactured after 1999 require ATF+4(r), a synthetic-based ATF only available through DaimlerChrysler.