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Advertising in 1940 proclaimed GM’s Hydra-Matic Drive Transmission as “the greatest advancement since the self-starter”

A black-and-white PR photo of a Cadillac Sixty-One coupe.

The1941 Cadillac Sixty-One five-passenger coupe was touted as ‘the mightiest, thriftiest, lowest-priced Cadillac V-8 ever built.’ (GM Media Archive)


In 1939, General Motors’ Cadillac and Oldsmobile divisions introduced breakthrough technology in the fully automatic Hydra-Matic Drive transmission. The transmission debuted for the 1940 model year.

“The Hydramatic was the first mass-produced fully-automatic transmission developed for passenger automobile use,” according to its page in Wikipedia.

Shiftless transmissions had been a focus during the 1930s. Then, as now, shifting a manual gearbox required more effort than most drivers cared to exert.

According to the Wiki story, automakers were in the fast lane to develop a transmission that reduces or eliminates the need to shift gears.

“At the time, synchronized gear shifting was still a novelty (typically only for higher gears). The exception was Cadillac’s breakthrough synchromesh fully synchronized manual transmission.”

The synchromesh transmission was designed by Cadillac engineer Earl A. Thompson and introduced in the fall of 1928.

Developing a Shiftless Transmission

By the early 1930s, Thompson had begun work on a “shiftless” transmission. His pioneering work led to creating a new department within Cadillac Engineering. Headed by Thompson, the transmission group included engineers Ernest Seaholm, Ed Cole, Owen Nacker, and Oliver Kelley.

“During 1934, the Cadillac transmission group had developed a step-ratio gearbox that would shift automatically under full torque,” according to Wikipedia. “This group of engineers was then moved into the General Motors Research Laboratory, building pilot transmission units during 1935-36. The transmission then went to Oldsmobile for testing.

a 1940 color print ad for General Motors' new Hydra Matic fully automatic transmission

All Cadillac models for 1941 could be optioned with the Hydra-Matic. (GM Media Archive)

The group effort led to the so-called Automatic Safety Transmission. The AST was a semi-automatic transmission using planetary gears and a conventional friction clutch. Drivers were still required to use the clutch to shift into or out of gear, but not between the two forward gears.

Oldsmobile offered the AST from 1937-1939, while Buick offered it only in 1938.

The next step was the Hydra-Matic. It combined the hydraulic operation of a planetary gearbox (for the automation of shifting) with a fluid coupling instead of a friction clutch, eliminating the need for de-clutching. The transmission would have four forward speeds plus reverse.

The transmission was named “Hydra-Matic Drive” and went into production in May 1939 for the 1940 model year.

Start of Hydra-Matic Production

The first Oldsmobiles so equipped were shipped in October 1939 in the Oldsmobile Series 60 and the Oldsmobile Series 70.

Oldsmobile was chosen to introduce the Hydra-Matic for two reasons:

  • Economies of scale — Oldsmobile produced more cars than Cadillac and Buick at the time, thus providing a better test base;
  • And to protect the reputation of Cadillac and Buick in case of a market failure of the new transmission. Advertising proclaimed it “the greatest advancement since the self-starter.”

In 1940, the Hydra-Matic was a $57 option (around $1,102 today). The price almost doubled for 1941, to $100 (or about $1,842 today). For the 1941 Cadillacs, the Hydra-Matic cost $125.

The transmission was a popular upgrade. Almost 200,000 cars had been optioned with the transmission by the time passenger car production was halted for wartime production in February 1942.