Earl A. Thompson

Thompson's 1918 invention of a synchromesh manual transmission using a tapered cone synchronizer to prevent gear clash (US Patent US1435430 in March 1922[2]) would make shifting a manual transmission faster, easier and safer. In April of 1922 Thompson, armed with drawings and data for a prototype synchromesh transmission, set out for Detroit to sell it to the automobile industry. But the automobile manufacturers were not impressed; their customers, he was told, were satisfied with transmissions just as they were. Thompson persisted. After several trips between Oregon and Detroit, and months spent improving the design, and two more patent applications,[3][4] he was finally able to arrange a meeting with Lawrence Fisher, managing director of Cadillac Motor Car Division and Ernest Seaholm, Cadillac's chief engineer. They were interested in the idea, and (in 1924) Thompson was retained as a consultant while the transmission was perfected[5] (10 models in all).

The first cars to use Thompson's synchromesh transmission design were Cadillac and LaSalle cars in 1928, then Buick 8's in 1931.[6] Thompson sold his synchromesh transmission patents to GM in 1924[7] and 1930 for a reported $1 Million.

Thompson became an employee of Cadillac Motor Car Division on September 1, 1929, and was appointed to be assistant chief engineer. Thompson continued improving the design of the synchronizer. In 1933. Thompson began working on the development of an automatically shifting transmission. Thompson left Cadillac in 1934 and joined the General Motors Corporation (GM) Engineering Department.[8]

In 1934 at the GM Engineering Department, Thompson became the project leader of a group of 4 engineers including Ralph F. Beck, William L. Carnegie, Walter B. Herndon, and Maurice S. Rosenberger. This group developed the Automatic Safety Transmission,[9] an optional semi-automatic transmission for some 1937-1939 Oldsmobile and 1938 Buick vehicles.[10]

In June 1936 a fifth engineer, "O.K." Oliver K. Kelley, joined Thompson's group; he was transferred from G.M.C. Truck and Coach Division where the development of a hydraulic torque converter drive for a transit bus was proceeding.[11] Thompson's group combined a fluid coupling with a unique hydraulically controlled, automatically shifting 4-speed planetary transmission, introduced as an option on 1940 Oldsmobiles as Hydra-Matic, the world's first mass-produced fully automatic transmission. The 1940 Hydra-Matic transmission would continue to be refined and produced for another 16 years, including wartime use in some military vehicles.