Automatic transmission fluid (ATF) is a specific type of transmission fluid used in vehicles with self-shifting or automatic transmissions. It is usually colored (can be red, green, or amber) to distinguish it from motor oil and other fluids in the vehicle in the event of a leak. The fluid is formulated for the special requirements of automatic transmission, such as valve operation, brake band friction, lock up torque converter, gear lubrication, power transfer, cooling, wear prevention, etc., making it the most complex multifunctional fluid in the automobile.
ATF is also used as a hydraulic fluid in older power steering systems, as a lubricant in some 4WD transfer cases, and in some modern manual transmissions in place of gear oils.
The history of automatic transmission fluids parallels the history of automatic transmission technology. The world’s first mass-produced automatic transmission, the Hydra-Matic 4-speed, was developed by General Motors (GM) for the 1940 model year. The Hydra-Matic transmission required a special lubricant GM called Transmission Fluid No. 1. for the Hydra-Matic Drive. This transmission fluid was only available at Oldsmobile, Pontiac, and Cadillac dealerships. Subsequent automatic transmission and fluid coupling technologies, along with difficulties with fluids in cold and hot temperature extremes led to a need for longer lasting, higher quality transmission fluids. Additionally, a better system of automatic transmission fluid distribution and marketing was necessary to ensure the long-term success of the new automatic transmission.
In 1949, GM released a new Type “A” fluid specification. It was an attempt to make GM automatic transmission fluid available at retailers and service garages everywhere. Every automatic transmission produced by any vehicle manufacturer used GM Type “A” transmission fluids in their transmissions from 1949-1958.
In 1959, Ford began releasing their own automatic transmission fluid specifications. From 1958-1968 many vehicle manufacturers continued to use the next GM automatic transmission fluid specification, the Type “A” Suffix “A” fluid in their transmissions. In 1966, Chrysler began releasing their own automatic transmission fluid specifications, calling it MOPAR Type A. ATF was the same color as engine oil through 1967. Aftermarket ATF of that time first became available with red dye as an aid in fluid leak detection shortly after the new GM DEXRON (Type B) was the first ATF to require red dye.
In the 1940s, 1950s, 1960s, and early 1970s, ATF contained whale oil as a friction modifier, antioxidant, anti-wear and rust and corrosion inhibitor. The moratorium on whale oil at that time prevented the continued production of older ATF such as the original 1967 DEXRON formulation (Type B), and the fluids which preceded it. Older GM (1940-1967), Ford (1951-1967, and Chrysler products (1953-1966) used GM Type A fluid or GM Type A Suffix A fluids; these fluids were no longer produced.
Through the 1970s, Ford transmissions were factory-filled with a fluid identified as ESW M2C33-F (FORD Type F ATF). To provide a fluid that would be available to the automotive service industry for service fill, oil companies and other than factory fill suppliers could develop fluids meeting the ESW M2C33-F specification and market these fluids under their own brand names but identified as Type F.
The second generation of FORD transmission fluid was released in 1974 as the factory fill specification, ESW M2C138-CJ. This fluid was developed to modify the vehicle shifting characteristics (more friction modifier for smoother shifting) and to provide considerable improvement in the oxidation resistance and anti-wear performance. From 1974-1987 no new fluids were developed by Ford. During this time DEXRON fluids approved by General Motors were considered acceptable for use in Ford automatic transmissions. With continuing changes and improvements in transmission design, a centrifugal lock-up torque converter clutch was developed and introduced in the Ford C5 transmission. To smooth driveline vibrations sensed by the occupant of the vehicle when the T/C clutch applied, Ford was forced to release the FORD factory fill specification ESP M2C166-H. Servicing transmissions with DEXRON fluids became unacceptable because DEXRON fluids at the time were not formulated to eliminate the shudder phenomenon. The fluids that could be used were a subset of the DEXRON fluids. The advent of Ford Type H as factory fill necessitated the development of a service fluid specification to match the performance expected from Type H. This resulted in the release of the MERCON specification in 1987.
The development of modulating and continuous slipping clutch torque converters drove FORD to develop the MERCON V specification. With added emphasis on developing new test procedures and performance requirements that verify the antiwear capabilities and anti-shudder characteristics of the fluid. The MERCON V specification was further modified some time prior to 2007 to make it reverse-compatible with MERCON. Ford has terminated all license agreements for the manufacture and sale of MERCON in favor of MERCON V in 2007.
Toyota continued using GM ATF, in most of their automatic transmissions until 2003. In 1988, Toyota began releasing their own automatic transmission fluid specifications, the new fluid was to be called Toyota Type T-II ATF. Nissan (Nissan Matic D) and Honda (Type Z-1) were quick to follow with their own specially formulated ATF discontinuing the DEXRON recommendations of the past.
In 1967, Ford produced the Type-F fluid specification. The Type-F specification was intended to produce a “lifetime” fluid which would never need to be changed. This was the first of many Ford “lifetime” fluids. The 1974 Ford Car Shop Manual reads “The automatic transmission is filled at the factory with lifetime fluid. If it is necessary to add or replace fluid, use only fluids which meet Ford Specification”. Since then, many other transmission manufacturers have followed with their own “Lifetime” automatic transmission fluids, but Ford Type F was the first (but certainly not the last OE) to make this dubious claim.
Since 1990 the proliferation of OE required “fill for life” ATF has grown to the point there are over 100 branded and required automatic transmission fluids currently in the automotive marketplace. This is a worldwide phenomenon with European and Asian OEM’s specifying their “required” OEM ATF. Some are difficult to find and others are extremely expensive and unique to the application. To make it even more complicated, there are now three automatic transmission types currently available making service fluid selection more critical than ever. We have the step automatic transmission (we are all familiar with) with 2-10 gears, the CVT transmission that continuously varies the drive output with sheaves and belts and the DCT (dual clutch transmission) that is essentially a manual transmission that automatically shifts the gears. Each type of ATF has its own unique requirements, using the wrong type of fluid can result in catastrophic failure of a transmission that can cost as much as $10,000.
Modern ATF consists of a base oil plus an additive package containing a wide variety of chemical compounds intended to provide the required properties of a particular OEM ATF specification. Most ATFs contain some combination of additives that improve lubricating qualities such as anti-wear additives, rust and corrosion inhibitors, detergents and dispersants, viscosity index improvers, seal swell additives, anti-foam additives and anti-oxidation compounds to inhibit oxidation, cold-flow improvers, pour point depressant and petroleum dye. All ATFs contain friction modifiers, except for those ATFs specified for some Ford transmissions and the John Deere J-21A specification.
Automatic transmission fluids have many performance-enhancing chemicals added to the fluid to meet the demands of each transmission. Some ATF specifications are open to competing brands, such as the common DEXRON specification, where different manufacturers use different additives to meet the same performance specification. These products are sold under license from the OEM responsible for establishing the specification. Some vehicle manufacturers will require “genuine” or Original Equipment Manufacturer (OEM) ATF. Most ATF formulations are open to 3rd party licensing, and certification by the automobile manufacturer at certified test labs designated by the OEM.
Each manufacturer has specific ATF requirements. Incorrect transmission fluid may result in transmission malfunction or severe damage; however, this most often occurs where the viscosity is extremely different, or the wrong type of ATF is used.
Understanding the needs and requirements of current and past automatic transmissions will be required for the service technician or rebuilder to successfully compete in todays complex and confusing automotive aftermarket. Between new technology like the EVs, and a challenging marketplace for parts and fluids that can change in the blink of an eye, technicians and shop owners need to be educated on making the right fluid choices when errors can be so costly.
