When Hydra-Matic was introduced by Oldsmobile in 1940, General Motors called it “the most important automotive advancement since the self-starter.” Here’s a closer look.

We want to choose our terms with care here. When we describe the 1940 Oldsmobile Hydra-Matic as the first truly automatic transmission in volume production—the first modern automatic, if you will—we also recognize all the worthy attempts that came before it. The Model T Ford, with its two-speed planetary transmission, was hard to beat for ease of operation, though it wasn’t a real automatic as we know it. Preselector transmissions, including Hudson and Cord in the USA, Wilson in the UK, and Cotal in France, came closer still.

But in the Hydra-Matic, there was no gear shifting required once the car was under way, and there was no clutch pedal. It was fully and truly automatic in operation, just like the automatic transmissions of today: Just place the selector in “Drive” and off you go. One difference worth mentioning: On the original Hydra-Matics, there was no Park position as such on the gear selector. The column indicator was marked “N-Hi-Lo-R” or similar.

In its internal operation as well, the Hydra-Matic was much like the automatics of the current day. There were three planetary gearsets to provide four forward speeds and reverse, with the gearchanges accomplished via clutches, bands, and hydraulic pressure. One key difference: While contemporary transmissions use a torque converter coupling to supply mechanical advantage for low-speed acceleration, the Hydra-Matic employs a straight fluid coupling with an effective ratio of 1:1—hence the need for four forward speeds. On the original Olds Hydra-Matic, the four ratios, first through fourth gears, were 3.66:1, 2.53:1, 1.44:1, and 1.00:1. Naturally, a variety of gearsets were used through the years to suit a wide range of specific applications.

Hydra-Matic Drive, as it was originally named, was developed by a team led by Earl Thompson (the creator of Synchromesh) that began as a Cadillac program in 1932 and was then moved to GM Central Research in 1936. An early semi-automatic version of the unit, using a similar planetary gear unit but with a standard friction-plate clutch instead of the fluid coupling, was offered in Oldsmobile and Buick cars in 1937-38 as the Automatic Safety Transmission.

In October of 1939 the full Hydra-Matic was introduced as a $57 option on the 1940 Oldsmobile, and Cadillac followed in 1941. Versions of the Hydra-Matic saw action in U.S. fighting vehicles in World War II, including the M5 Stuart and M24 Chafee tanks. Pontiac (photo above) adopted the Hydra-Matic in 1948, but the Buick and Chevrolet divisions opted to develop their own automatics. (See our features on the Buick Dynaflow here and the Chevrolet Powerglide here.)

As the first automatic that was widely available to the public, Hydra-Matic caught the Kleenex effect and for a time, became a popular generic name for any automatic gearbox. And indeed, GM made the Hydra-Matic transmission available to a number of automakers, including Hudson, Nash, Lincoln, Kaiser-Frazer, Willys, and even Rolls-Royce. While both Oldsmobile and Cadillac claimed the innovation in their advertising, or at least implied it, Hydra-Matic was essentially a GM corporate development. However, both divisions participated in the vehicle integration and production process.

Hydra-matic saw continual development through the years, including a major internal redesign for 1956 to soften the unit’s harsh gear changes, especially on the 1-2 and 2-3 upshifts. Rugged and reliable, the unit was widely offered in light trucks and was even popular in drag racing in the ’60s. But on the downside, the Hydra-Matic was expensive to produce, extremely heavy due in part to its cast-iron case, and lacked a torque converter. After 24 years in production, the original Hydra-Matic was phased out in 1964, but the Hydramatic name (with the hypen removed) has lived on at GM into the 21st century, but on a series of entirely different transmission families.