By early 1939, Oldsmobile had built 5,000 preproduction cars with a new version of the AST, dubbed Hydra-Matic Drive. Internally, Hydra-Matic was very similar to the AST, but used a third planetary gearset rather than spur gears for reverse. Two oil pumps, one driven by the engine, the other off the transmission output shaft, provided operating pressure for the control valve body. A fluid coupling replaced the conventional clutch; Oliver Kelley, who was the lead designer and in whose name the patent was filed, dubbed the coupling a “fluid turbo clutch.” The coupling had an unorthodox feature that was to become a Hydra-Matic signature: To prevent the car from creeping forward at idle, the engine flywheel drove the fluid coupling impeller through the front planetary gearset rather than directly. As a result, the impeller was always turning slower than was the engine, reducing creep.
As with the Automatic Safety Transmission, Low range provided automatic shifting between first and second gear. Drive functioned much like the AST’s High range, but the governor had been reworked to shift automatically through all four forward speeds. The two-three shift was still mechanically complex and tended to be jerky if the bands and linkages were not in perfect adjustment, but there was no clutch pedal and no need for manual shifting except to select reverse or neutral.
Unlike the Automatic Safety Transmission, Hydra-Matic was not built by Buick. In early 1939, GM, correctly sensing that the new transmission would be a big hit, established a new Detroit Transmission Division to manufacture Hydra-Matic. Production development began in May and Hydra-Matic went on sale that October as a regular production option for all 1940 Oldsmobiles. At launch, the retail price for the option was only $57, which was actually $18 less than the old AST.
As Oldsmobile’s none-too-modest advertising proudly declared, Hydra-Matic was a paradigm-changing innovation. Whatever its problems — which on early cars included engine surge, a tendency to harsh shifts, and problems with the transmission’s special “Hydra-Matic Drive Fluid” — Hydra-Matic offered painless two-pedal driving. For American drivers, most of whom had never been enamored of manual shifting to begin with, Hydra-Matic was a compelling proposition, attracting even customers who’d been burned by previous semiautomatic transmissions.
As was GM policy at that time, Oldsmobile had exclusive use of Hydra-Matic for one year in recognition of the division’s considerable efforts (and expenditures) in developing the transmission. When that exclusivity period expired, Buick still wanted nothing to do with Hydra-Matic, which Buick chief engineer Charles Chayne nicknamed “Hydra-Jerk,” but Cadillac added Hydra-Matic to its options list in 1941. Despite higher prices — now $100 on Oldsmobiles and $125 on Cadillacs — more than 40% of Oldsmobile buyers and about 30% of Cadillac customers opted for the self-shifting transmission.
By the time the War Production Board halted civilian automobile production in February 1942, the Detroit Transmission Division had delivered almost 215,000 Hydra-Matic transmissions. Hydra-Matic’s influence and popularity would only increase during and after the war.
Even as production of passenger cars was winding down, the American auto industry was rapidly converting to military production. The conversion was supervised by William (“Big Bill”) Knudsen, who had been president of General Motors from 1937 to 1940, so naturally GM played a major role in the war effort. (Ironically, 25 years earlier, Cadillac founders Henry and Wilfred Leland had resigned from General Motors after then-president Billy Durant refused to become involved with military production.)
In 1941, before the United States entered World War II, the principal U.S. light tank was the M-3 Stuart, manufactured by the American Car & Foundry Co. The M-3, which British armor units nicknamed “Honey,” weighed 14 tons (12.7 metric tons) and was armed with a 37mm cannon and four 0.30-caliber (7.62mm) machine guns. It was powered by a single seven-cylinder Continental W-670 radial engine with 262 gross horsepower (195 kW). By 1942, the Stuart was in service in North Africa and the Pacific theater with the British Army, the U.S. Army, and the United States Marine Corps.
The gasoline-powered Continental engine was in short supply in 1941-1942, forcing some Stuarts to adopt less-powerful diesel engines. In late 1941, Cadillac proposed a new M-3 variant that would substitute two of the division’s V-8 engines for the Continental unit. The two engines were more-or-less stock 346 cu. in. (5,676 cc) Cadillac V-8s, each rated at 148 gross horsepower (110 kW) and each driving one tread via a beefed-up Hydra-Matic transmission called Torq-Matic. The engineer responsible for overseeing this project was one Edward N. Cole, later to become chief engineer of Cadillac and Chevrolet and eventually president of General Motors.
The redesigned tank, designed M-5 Stuart VI, entered production in March 1942. With the dual engines, heavier armor, and other modifications, it was around 5,100 lb (2,313 kg) heavier than the M-3A1, but the twin Cadillac engines provided a comparable top speed. Around 6,800 Cadillac-engined M-5s and M-5A1s were built along with about 1,800 M-8 self-propelled howitzers, which shared the same chassis.
By 1943, it was clear that the M-5 was too lightly armed for the European theater. In April, Cadillac began work on an enlarged version sharing the M-5’s powertrain but trading the 37mm cannon for a 75mm gun, the new lightweight M6 (a.k.a. T13E1) cannon also used on the North American B-25H Mitchell bomber. The new tank, dubbed M-24 Chaffee, was accepted for production in April 1944 and reached frontline service in November. More than 4,300 were built by the end of the war and some remained in service until the late eighties. There were also a number of M-24 derivatives sharing its chassis, engines, and automatic transmissions, including the M-19 gun carriage and M-37 and M-41 howitzer carriages.
Military service brought no dramatic design changes to the civilian Hydra-Matic transmission, but the development of Torq-Matic forced GM to resolve many of Hydra-Matic’s early teething problems and later allowed postwar Cadillac and Oldsmobile advertising to boast that Hydra-Matic had been proven in combat. When civilian production resumed, Hydra-Matic was also among the features of GM’s “Valiant” models, which had special driver controls, developed by Oldsmobile, for use by disabled veterans.
Hydra-Matic really took off during the postwar boom. Buick and Chevrolet still disdained it, opting to develop their own torque converter automatics, but Pontiac reluctantly adopted Hydra-Matic in 1948. The transmission was enormously popular despite its high prices, which in 1948 ran to $174.25 on a new Cadillac and $185 on an Oldsmobile or a Pontiac (the latter equivalent to more than $1,600 in 2010 dollar). That year, 73% of Pontiac buyers, 97% of Cadillac, and nearly that many Oldsmobile buyers opted for Hydra-Matic.
By 1949, it was becoming clear that not only was automatic transmission a marketing advantage, lacking an automatic was a serious competitive handicap. While Hydra-Matic was never the smoothest of transmissions under the best of conditions and imposed penalties in both performance and fuel economy, many customers didn’t care. Critics like Mechanix Illustrated reviewer Tom McCahill disdained automatics, but American buyers were willing to accept the drawbacks if it meant not having to shift.
Other automakers were soon forced to follow GM’s lead. Ford and Studebaker turned to Borg-Warner to develop three-speed torque converter transmissions while Packard introduced its proprietary Ultramatic in May 1949. Chevrolet launched its first Powerglide transmission late that year for Chevy’s 1950 models.
The Detroit Transmission Division built its millionth Hydra-Matic in January 1949. Not satisfied with that volume, GM began selling Hydra-Matic to automakers who couldn’t afford to develop their own automatics. Curiously enough, one of the first customers was Lincoln-Mercury, which added Hydra-Matic as a Lincoln option mid-year; Ford’s new Fordomatic/Merc-o-Matic wasn’t yet ready and in any case didn’t have the torque capacity for the big Lincoln V-8. Other Hydra-Matic customers included Nash, Hudson, and Kaiser-Frazer. Most outside users didn’t bother to conceal the Hydra-Matic’s GM origins, happy to take advantage of its reputation and name recognition.
With so many new customers, it took GM less than two years to sell another million Hydra-Matics, making the Hydra-Matic the most successful automatic transmission in the world.