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A look at changes in automatic transmission fluid

Wednesday, September 26, 2018 - 07:00
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Earlier this year Ford donated a brand new 10R80 10-speed automatic transmission from a 2017 Ford F-150 to our school for training purposes. I was very excited because this is one of the newest transmission technologies available. As I positioned it on my workbench I looked across the shop at another transmission with incredible technology, the 1940 General Motors Hydra-Matic 4-speed, the world’s first mass-produced automatic transmission.

Both of these amazing transmissions as well as the hundreds of others that have come along in the past 78 years were designed to use an Automatic Transmission Fluid (ATF) that had been customized for that very transmission. Without the specified ATF, these transmissions cannot perform as designed. This article will focus on the evolution of ATF and the reasons why using the right fluid can make a big difference. I know that some of you do not believe that the factory specified fluid is the best choice for your transmission, but if you will continue reading, you may change your mind by the end of this article.

Figure 1 - 2017 Ford F-150 10R80 10-Speed Automatic Transmission

Warning – Historical content!

To understand the evolution of ATF, it is helpful to have a basic understanding of the development of the automatic transmission. Prior to 1940, manually shifted transmissions were the only option for the majority of automobiles and trucks available. Prior to 1928, none of those transmissions contained synchronizers. This means that every shift could take up to 10 seconds to complete because the driver had to use a difficult process called Double Clutching to avoid gear clash.

A young engineer named Earl A. Thompson designed and patented the first synchronized manual transmission in 1922.  Cadillac purchased Thompson’s patents and with Thompson’s help offered refined version of it as the Synchro-Mesh Transmission in 1928 Cadillacs. This invention was only the first step towards Thompson’s goal of designing a fully automated transmission.

1938-1939: Strange beginnings —motor oil

By 1934 Thompson’s group had developed a 4-speed transmission called the Automatic Safety Transmission (AST). It was given that name because clutch operation was reduced to one third of that required by a conventional transmission. The AST used the same seasonal grade of motor oil as the engine for lubrication and hydraulic functions.

In the 1930s, crude oil was refined into a Group I base oil by a process called solvent refining. Motor oil was created by combining chemical detergents (additives) with the base oil to prevent sludge and varnish buildup. 

1939-1941: Specialty transmission fluids are developed

For the 1939 model year, Chrysler offered the “Fluid Drive.” This car had a three-speed manual transmission connected to a conventional clutch. The clutch was connected to the engine through a sealed fluid coupling. Depressing the clutch pedal was not needed unless the driver desired a different transmission gear. The fluid coupling was partially filled (80 percent) with a special Mopar Fluid Drive Fluid. The transmission gearbox used regular S.A.E. 80-160 gear oil.

Figure 2 - 1939-1951 Mopar Fluid Drive Fluid

The world’s first mass-produced fully automatic transmission, the Hydra-Matic Drive, was released for 1940 model year Oldsmobiles. This was the first transmission that combined several new and existing technologies (planetary gears, bands, servos, governor, throttle valve, valve body, and fluid coupling) into one fully automatic package.

The Hydra-Matic Drive used a specialized lubricant called GM Transmission Fluid No. 1. By using the term "fluid" rather than "oil" they hoped to discourage the previously accepted practice of using S.A.E 20 engine oil. The only source of this new transmission fluid was at Oldsmobile dealerships. In 1941, Cadillac also used the Hydra-Matic Drive.

Figure 3 - Two examples of GM Hydra-Matic Fluid 1940-1949

Oldsmobile and Cadillac recommended the fluid be checked every 1,000 miles and changed every 5,000 miles. The Hydra-Matic drive was a huge success with over thirteen million transmissions being produced over the next 16 years.

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