Shift Pointers
- Subject: History of the GM Hydramatic transmission
- Essential Reading: Rebuilder, Diagnostician
- Author: Pete Luban, Transmission Digest Contributing Editor
I’m going to do something a little out of the ordinary this time instead of the usual (or unusual) tech article that you typically see in this column.
This all came about from a technician who was working on a cast-iron Hydramatic in a vintage 1955 Cadillac. During the phone conversation the technician mentioned that with all the late-model electronically controlled vehicles that come through his shop, it felt strange working on a version of the first automatic transmission ever put into a car or truck, to which I answered, “I don’t think the cast-iron hydro was the first automatic transmission.”
The technician said he never knew that any automatic transmission existed prior to the cast-iron hydro and then added that this might make for some interesting reading in a magazine article. So, here we go.
The first recorded use of an automatic transmission in a motor vehicle was actually in France, by an inventor named Johabert L.H. Maugras. His Automatic Split-Torque Drive was actually a type of infinitely variable transmission. Sound familiar? Yep, it was a CVT, and this took place in 1897. However, Maugras’ transmission never made it to reality because of the technology of the times being inadequate.
Now for us here in the States, the first use of an automatic transmission in a motor vehicle took place in Massachusetts. Inventor Thomas J. Sturtevant came up with something called the Sturtevant Two Speed Automatic Unit in 1904. This design used two clutches, one for low gear and one for high gear.
The biggest problem with the Sturtevant transmission was its inability to stay in high gear at lower vehicle speeds. It would totally fall out of gear when engine braking was most needed (usually down hill), and, of course, in those days the brakes were virtually ineffective under these conditions, which resulted in “Mr. Toad’s wild ride!”
Believe it or not, 44 other transmissions considered automatic actually were invented before the GM cast-iron Hydramatic went into production in 1939 for use in the 1940 Rocket Oldsmobile. Cadillac followed next by using it in the 1941 models. So the transmission used in the 1955 Cadillac my technician was working on was actually nearing the end of production in the U.S. although it did have continued use in GMC trucks, Hudson, Lincoln, Frazer, Kaiser, Nash and Rolls Royce. Rolls Royce, under a licensing agreement with GM, used a variation of the Hydramatic in right-hand-drive models. This was a different animal, and almost none of the parts in the left-hand-drive transmission would interchange with those in the right-hand-drive model.
The cast-iron Hydro also served in the military in deuce-and-a-halfs (21/2-ton trucks, for you “younguns”), and a variation of the Hydramatic was used in tanks during WWII.
Cadillac, Pontiac and Oldsmobile divisions continued use of the cast-iron Hydro up to 1955 with the exception of the 1953 model year. On Aug. 12, 1953, the Hydramatic plant in Livonia, Mich., was severely damaged by fire, and until Hydramatic production could be resumed, Cadillac and Oldsmobile used Buick’s Dynaflow and Pontiac used Chevrolet’s cast-iron Powerglide.
For the 1956 model year Cadillac, Oldsmobile and Pontiac divisions ended use of the cast-iron Hydramatic and replaced it with the Jetaway, but that’s another story.
My apologies to any automotive or military historians for any inaccuracies that I may have committed, as most of this article came from memory – which seems to become more unreliable as time goes on.
