Hydramatic

Hydramatic (also known as Hydra-Matic) is an automatic transmission developed by both General Motors' Cadillac and Oldsmobile divisions.

Introduced in 1939 for the 1940 model year vehicles, the Hydramatic was the first mass-produced fully-automatic transmission developed for passenger automobile use.

This same group of engineers was then moved into the General Motors Research Laboratory, building pilot transmission units during 1935–36 which were then handed to Oldsmobile for testing.

The HydraMatic was designed to combine the hydraulic operation of a planetary gearbox (allowing much shifting to be automated) with a fluid coupling instead of a friction clutch, eliminating the need for de-clutching.

The transmission would have four forward speeds (3.82:1, 2.63:1, 1.45:1, and 1.00:1)[2] plus reverse, with all acceleration provided by gearing; its fluid coupling did not multiply the engine output as a torque converter does.

Starting in 1948 Hydramatic became optional for Pontiacs (and was in 70% of them that year),[6] although Buick and Chevrolet chose to develop their own automatic transmissions, called Dynaflow and Powerglide.

As a result, Oldsmobiles and Cadillacs during the downtime were assembled with Buick's Dynaflow transmission, while Pontiacs used Chevrolet's Powerglide, both two-speed torque-converter units.

Non-GM makes that bought Hydra-Matics from the corporation, including Ford Motor Co.'s Lincoln division and independent automakers Hudson, Kaiser, and Nash ended up looking for other sources of automatic transmissions as well, with Lincoln using the Borg-Warner-designed Ford-O-Matic transmission, while other automakers also switched to automatics from Borg-Warner during the downtime.

About nine weeks after the Livonia fire, GM opened up a new source for Hydra-Matic production at Willow Run, Michigan.

Evolving by the pressure of industrial competition from other manufacturers such as Studebaker's three-speed lock-up torque converter co-designed by Detroit Gear (a division of Borg-Warner), named DG 200/250, and Packard's dual-range two-speed lock-up torque converter coupled Ultramatic, GM's Hydra-Matic underwent several revisions through 1955, before being gradually replaced by the substantially redesigned Controlled-Coupling HydraMatic (also called Jetaway, by Oldsmobile, and StratoFlight, and later Super Hydra-Matic, by Pontiac, or 315 HydraMatic, by Cadillac, or Dual-coupling Hydra-Matic) in 1956.

Chevrolet Division's light truck line used the less-than-adequate Powerglide all through the 1960s until Turbo-Hydramatic was made standard in 1969.

1964 Turbo-Hydramatic production used a selector quadrant similar to Chevrolet's Powerglide in that there was only one "Drive" position and a "Low", although it was a true three-speed unit.

The front pump was a variable displacement vane unit driven from the fluid coupling housing, which meant oil pressure would be available immediately upon starting the engine.

That is, the input torus of the fluid coupling ran at a slower speed than the engine, due to the reduction of the forward gear assembly.

[5] The fluid coupling now only handled about 25 percent of the engine torque, reducing slippage to a negligible amount.

As the transmission's seals and other elastomers aged, the hydraulic control characteristics changed and the 2-3 shift would either cause a momentary flare (sudden increase in engine speed) or tie-up (a short period where the transmission is in two gears simultaneously), the latter often contributing to the failure of the front band.

Much of the difficulty in staging a "clean" 2-3 or 3-2 shift in any cast-iron Hydramatic was the changing elasticity of the governing springs in the valve bodies.

Even ambient temperature would affect this variable, so that a Hydramatic that would shift perfectly on a summer's day would usually exhibit 2-3 "flare" when cold.

Another long-standing driver complaint would be "flare" when trying to get a "3-2" downshift when going around a corner, which usually resulted in a neck-snapping jolt upon band application.

This worked better as the anchor would not grind on the external teeth if that ring gear were turning (that is unless the engine stalled as reverse was engaged).

With the engine off, this brake band acting on the rear unit ring gear had a tremendous mechanical advantage.

The first-generation Hydramatic (not the Controlled-Coupling version that succeeded it in 1956) did not have a separate park position as found in modern automatic transmissions.

The driver had to shut off the engine and then place the transmission in reverse in order to lock the driveline to prevent the car from moving.

Early 1940 model Oldsmobiles with Hydra-Matic Drive could be started with the transmission selector lever in any position.