Hydramatic (also known as Hydra-Matic) was an automatic transmission developed by both General Motors' Cadillac and Oldsmobile divisions. Introduced in 1939 for the 1940 model year vehicles, the Hydramatic was the first fully automatic mass-produced transmission developed for passenger automobile use.

History

During the 1930s, automakers sought to reduce or eliminate the need to shift gears. At the time, synchronized gear shifting was still a novelty (and confined to higher gears in most cases), and shifting a manual gearbox required more effort than most drivers cared to exert. The exception here was Cadillac's break-through synchromesh fully synchronized manual transmission, designed by Cadillac engineer Earl A. Thompson and introduced in the fall of 1928.

Cadillac, under Thompson, began working on a 'shiftless' transmission in 1932, and a new department within Cadillac Engineering was created, headed by Thompson and including 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. This same group of engineers was then moved into GM Central Research, building pilot transmission units during 1935-36 which were then handed to Oldsmobile for testing.