Hydra-Matic Transmission

By John Linhardt

On March 1st 1941, Cadillac announced the availability of the Hydra-Matic Transmission as an option on all series of their cars. The automatic was not a completely “new” thing that year, as a form of automatic had appeared on Oldsmobile in 1937 thru 1939 and Buick in 1938 on Series 40 only.

The predecessor to the Hydra-Matic Transmission was a self shifting planetary transmission, with a manual clutch which was depressed at stops and changed the range of the unit from Forward to Reverse. Reverse was accomplished by a sliding gear set, much as it is on a conventional manual transmission. In 1940, a “fully automatic’ transmission took the place of the 1937 to 1939 self shifting transmission, eliminating the friction-clutch and its controls.

I owned two 1941 Cadillacs with Hydra-Matic, and never had any problems. One had to know two secrets. 1: to get to reverse, the lever had to stay in “low” momentarily and not a “one-shot” to reverse, otherwise there would be a big “grind” noise. 2: An intense “meow” emitted from the 1941 transmission front pump, and it varied in pitch as the engine increased its torque and speed. This is the same for 1941-1942, but was corrected on 1941-42 Cadillacs. So collectors have put later ‘46-’51 transmissions in their cars to solve this. The 1952 would work, but that’s a dual range, so it would not look original on the steering column.

This “Hydra-Matic” was so strong, the 2 1/2 ton military truck I drove in the National Guard was Hydra-matic and so were WWII tanks and M-114 armored personnel carriers and U.S.M.C. Marginal Terrain Vehicles used the Hydra-Matic. Lincoln, Rolls-Royce, Hudson and others also used the Hydra-Matic. A problem, arose when on 8/12/53, the only Hydra-Matic transmission factory at Livonia Michigan went on fire, and burnt to the ground. Two employees were killed, but in 90 days, Production began again at a former Studebaker-Packard plant in Michigan. This crises crippled 1953 GM production as Power-Glide and Dyna-Flow had to be used in other GM brands, and a Cadillac with Dyna-Flow was a “bomb” with major me-
chanical and leakage problems. Later GM replaced those transmissions, when available, at no

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