Who invented the synchromesh transmission in 1919?

Earl Avery Thompson is credited with inventing the synchromesh transmission in 1919. His innovation addressed a major weakness of early manual gearboxes: the driver had to match the speeds of the gears before engagement, or the dog teeth could clash and produce the familiar grinding noise.

Thompson’s design used friction surfaces to bring the rotating parts close to the same speed before the dog clutch locked them together. That made gear changes smoother and reduced the need for drivers to double-clutch or manually “blip” the throttle during shifts. Historical accounts sometimes date Thompson’s initial work or patent activity to 1918, while quiz references commonly state 1919 for the invention.

The technology was not immediately universal. Thompson’s patents were acquired by General Motors, and Cadillac eventually put the design into production in 1928, with LaSalle also receiving it. Later synchronizer systems, including Porsche’s split-ring design patented in 1947, refined the principle. Synchromesh became standard gradually, and many early cars synchronized only some forward gears.