The preslector gearbox

[KentTeffeteller]

Originally Posted by benman94

Some of the history of GM's Hydramatic has been a bit bungled.

The Hydramatic started as a Cadillac development in the early 1930s, and was continued under the auspices of Central Research. Cadillac, Olds, and Buick lent engineers out for the early development work. This lead to the Automatic Safety Transmission that required one to operate a clutch to move between reverse, neutral, and the forward position. Once in the forward position, you could switch between forward gears at will without using the clutch. This was offered for a model year or two on Olds and Buick. It wasn't exceptionally popular.

It was decided to give the fully automatic Hydramatic transmission to Olds in late 1939 for the 1940 model year in case the design was a flop. This pissed off the Buick engineers, and thus they waited for Oliver Kelley's transmission, which would eventually become the Buick Dynaflow transmission. The Dynaflow saw some use during the war in military applications and would become and option on Buicks starting in 1947 for the 1948 model year.

Olds and Cadillac engineers were able to iron out some minor flaws with the Hydramatic, and it became an option in late 1940 for the 1941 model year on Cadillac. The Hydramatic was a hit in the prewar years and would return when postwar production resumed at both divisions. After the war, Pontiac was given the Hydramatic as well. The original Hydramatic is actually fairly efficient for an early automatic. The Olds 303 V8 paired with a Hydramatic transmission was pretty good on gas for the time.

Chevrolet would introduce the Powerglide transmission, which was a tangential development from the same work done by Kelley on the Dynaflow. They're extremely similar to one another, but were developed more or less separately from 1946 onward. The Powerglide is fairly efficient for an early automatic; the Dynaflow turned Buicks into even bigger gluttons. Then I suppose if one could afford a Buick you wouldn't have been worrying about the price of gas either...

GMC trucks inherited the Hydramatic from Pontiac in the early 1950s as they shared engineering talent often, due mostly to proximity. It was beefed up and modified a bit for use in light duty trucks, but is otherwise more or less the same as any other post-war Hydramatic.

Chevrolet was originally supposed to receive a larger Dynaflow transmission for their trucks; such a design had been worked out during the war for the Hellcat tanks, etc. But due to the sharing of components between GMC and Chevrolet trucks that already existed, it was decided to simply use the same truck Hydramatic for both makes.

Another reason GMC got Hydramatic was due to GMC using Pontiac engines in some of the trucks, especially V8 engines when GMC offered a V8. Those two divisions seemed to share components a lot.