Hydra-Matic - First Mass-Produced Fully Automatic Transmission

The modern automatic transmission was not the result of a single invention. Many auto industry companies independently provided substantial contribution to automation of car transmissions. The first prototype of automatic gearbox was designed in 1921 by Alfred Horner Munro. Being a steam engineer, Munro created his mechanism operating with compressed air rather than hydraulic oil, so it lacked power and was not commercially manufactured.

GM then developed the 1-st automatic transmission using hydraulic oil in the 1930’s, and unveiled the “Hydra-Matic” transmission in 1940. The Hyrda-Matic 4-speed planetary gearbox was designed by a GM engineer Earl Thompson. The original Hydra-Matic was a crucial innovation in the auto industry. It wasn’t the first automatic transmission, but it was the first one that actually produced expected results and its commercial effectiveness cleared the way for following auto-shifting solutions. GM’s product combined a fluid coupling, planetary gears, an internal hydro pump, and fluid pressure to activate the clutches and shift the gear ratios. The Hydra-Matic did have its problems – perhaps the most noteworthy one was jerky shift from second to third that earned the nickname “Hydra-Jerk”.

The Hydra-Matic was significantly upgraded during 1955, but the basic design remained the same during its long life span. GM replaced the Hydra-Matic in 1956 with the Jetaway.