The first transmissions were manual. This required the driver to shift between gears so that a vehicle can be speeded up or slowed down while the engine rotated within an optimum speed range. For many decades, manual transmissions were tricky to drive but good enough for most drivers. Some just never liked the coordinated shifting and clutching procedure involved, though. The car manufacturers were quite cognizant of this issue, and as a result, many were privately experimenting with self-shifting transmissions during the 1930s.

The Automatic Safety Transmission

The first to release a self-shifting transmission was General Motors. Released in 1937, their “Automatic Safety Transmission”(AST) used planetary gears and a conventional friction clutches. The ASTs were a trifle kludgy and never inspired the driving public.

The Hydro-Matic Transmission

In 1938, Oldsmobile became the first American production car outfitted with a true automatic transmission. Called the Hydro-Matic, it was developed by legendary GM engineer Earl Thompson. The secret behind the Hydro-Matic was a device called a torque converter, which essentially eliminated the clutch. By 1941, the Hydro-Matic transmission was available in most GM models.

As it turns out, the Hydro-Matic got famous fast as it came to market just in time to help out the Allies in World War II. It was used in many military applications, including the M5 Stuart and the M24 Chaffee light tank. After the war, the transmission had been so improved and battle hardened that other auto manufacturers purchased them. These included Hudson, Frazer Nash, Willys, Rolls-Royce, Nash Rambler, Kaiser, Lincoln and Bentley.

Even into the 1990s, the Hydro-Matic was still being used in modified versions for drag racing and hotrod applications. One fellow, in particular, made the “B&M Hydro” a mainstay of hot rodders for decades: Andy Granatelli. In fact, his modified Hydro-Matic was the only automatic transmission to ever be used in Indy Car racing.

The Fluid Drive

Meanwhile, Chrysler Corporation was working on its own automatic transmission called the Fluid Drive, which was introduced in 1939. A quick phone call to the Chrysler experts at Len Stoler of Westminster, a local Dodge, Chrysler, Jeep Ram dealer in Westminster, MD revealed that Fluid Drive was similar to GM’s AST transmission. In other words, it was really a conventional manual transmission that used a fluid coupling. Like General Motor’s AST transmission, it had limited success, but Chrysler moved ahead quickly, and in 1942, they produced a semi-automatic transmission and introduced their famous two-speed PowerFlite in 1954.

Computers Get Involved

The automatic transmissions of the 1940s and 50s were all hydraulic affairs. The shifting logic was controlled by a complex network of oil channels and shifting valves. In the late 1980s, as onboard computers became more common, came the introduction of electronic controls for automatic transmissions. Solenoids and sensors are integrated with multiple onboard computers to control shifting and gear ratios. This has allowed engineers to fine-tune their transmissions for peak performance and high gas mileage.

Wasting Gas? Not Anymore

In the past, automatic transmissions were nice to have but their convenience came at a cost: reduced gas mileage. You could count on an automatic transmission getting 10-20% less mileage than the same car with a manual. This has all changed, though. Five-speed, six-speed, seven and even ten-speed transmissions are currently being installed in automobiles, and these transmissions are getting the same mileage as their manual counterparts. The old argument that automatics “waste gas” simply isn’t true anymore.