Hydramatic - History

History

During the 1930s, automakers sought to reduce or eliminate the need to shift gears. At the time, synchronized gear shifting was still a novelty (and confined to higher gears in most cases), and shifting a manual gearbox required more care than most drivers cared to exert. The exception here was Cadillac's break-through synchromesh fully synchronized manual transmission, designed by Cadillac engineer Earl A. Thompson and introduced in the fall of 1928.

Cadillac, under Thompson, began working on a 'shiftless' transmission in 1932, and a new department within Cadillac Engineering was created, headed by Thompson and including engineers Ernest Seaholm, Ed Cole, Owen Nacker, and Oliver Kelley. During 1934, the Cadillac transmission group had developed a step-ratio gearbox that would shift automatically under full torque. This same group of engineers was then moved into GM Central Research, building pilot transmission units during 1935-36 which were then handed to Oldsmobile for testing.

The Automatic Safety Transmission (AST) was a tangent outgrowth of this work. The AST was a semi-automatic transmission using planetary gears and a conventional friction clutch, requiring the driver to use the clutch to shift into or out of gear, but not between the two forward gears. Oldsmobile offered the AST from 1937-1939, while Buick offered it only in 1938.

The HydraMatic was designed to combine 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) plus reverse, with all acceleration provided by gearing; its fluid coupling did not multiply the engine output as a torque converter does. (In this way, it was less sophisticated than the 1924 Vulcan prototype, which had a torque converter.) It incorporated a parking pawl which was engaged when the shift selector was placed in reverse with the engine off. There was no separate Park position as found with modern transmissions.

The result, dubbed "Hydra-Matic Drive," went into production in May 1939 for the 1940 model year. The first Oldsmobiles so equipped were shipped in October 1939. Oldsmobile was chosen to introduce the Hydra-Matic for two reasons: economies of scale—Oldsmobile produced more cars than Cadillac at the time, thus providing a better test base—and to protect the reputation of Cadillac in case of a market failure of the new transmission. Advertising proclaimed it "the greatest advance since the self-starter."

In 1940, the Hydra-Matic was a $57.00 option, rising to $100.00 for 1941. In 1941, it also became an option on Cadillacs for $125.00. Almost 200,000 had been sold by the time passenger car production was halted for wartime production in February 1942.

During the war, the Hydramatic was used in a variety of military vehicles, including the M5 Stuart tank (where two of them were mated to twin Cadillac V8 engines) and the M24 Chaffee light tank. The extensive wartime service greatly improved the postwar engineering of the transmission, later advertised as "battle-tested."

Starting in 1948 Hydramatic became optional for Pontiacs (and was in 70% of them that year), although Buick and Chevrolet chose to develop their own automatic transmissions. One million Hydramatics had been sold by 1949. In the early 1950s various manufacturers without the resources to develop a proprietary automatic transmission bought Hydra-Matics from GM. Users included:

• 1951–1957 Hudson
• 1950–1957 Nash
• 1950-1957 Nash Rambler
• 1958-1960 Rambler American (AT&T associated company fleet units only)
• 1951 Frazer
• 1951–1955 Kaiser
• 1954–1955 Willys
• 1949–1954 Lincoln

In 1952, Rolls-Royce acquired a license to produce the HydraMatic for Rolls-Royce and Bentley automobiles. It continued production through 1967.

A massive fire that destroyed GM's Hydramatic plant in Livonia, Michigan on August 12, 1953 left the corporation and the three divisions that used this transmission scrambling for other sources of automatic transmissions to complete that year's model year production. 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 Hydramatics 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 Hydramatic production at Willow Run, Michigan. By the time the 1954 models debuted in late 1953, Hydramatic production had returned to normal levels and all '54 model Cadillacs, Oldsmobiles and Pontiacs with automatic transmissions were once again equipped with Hydramatics.

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 Hydramatic underwent several revisions through 1955, before being gradually replaced by the substantially redesigned Controlled Coupling Hydramatic (also called Jetaway or dual-coupling Hydramatic) in 1956.

The new four-speed Jetaway transmission incorporated a secondary fluid coupling and a pair of sprag clutches in place of the former friction clutch and brake bands, shifting in part by alternately draining and filling the secondary coupling. It was a later version of GM's "dual range hydra-matic",first introduced in some 1952 models. The dual range feature allowed the driver to hold the transmission in second or third gear until the maximum allowable upshift points, for improved performance in traffic or in mountain driving. The new, dual coupling transmission also incorporated a separate park position, falling in line with other automatic transmissions of the day.

With shifts taking longer and at higher engine speeds, however, performance and fuel efficiency suffered,compared to the original four-speed Hydra-matic. On the plus side, Jetaway was substantially smoother than the original Hydramatic, but also more complex and expensive to produce, as well as less efficient.

In 1961, a somewhat less complex, but also far less reliable three-speed Roto Hydramatic also dubbed the "Slim Jim" Hydramatic (in which the "dump and fill" shifting principle was retained) was adopted for all Oldsmobiles as well as Pontiac's full-sized Catalina, Ventura, and Grand Prix models, while all Cadillacs and Pontiac's Bonneville and Star Chief models retained the older four-speed "Jetaway" unit (not to be confused with the two-speed Jetaway automatic used in various Buick, Olds and Pontiac intermediate cars from 1964-1969). Both of those Hydramatic transmissions were ultimately replaced by a new three-speed torque converter automatic transmission called Turbo-Hydramatic in 1964 and 1965, whose design was more similar in principle to the Chrysler TorqueFlite and the '51 Borg Warner designed Ford Cruise-O-Matic than the fluid coupling Hydramatic the "Turbo" replaced.

The original Hydramatic continued to be used in light trucks and other commercial vehicles until 1962. It was subsequently replaced in that role by Chevrolet Division's Powerglide (where it was dubbed "Pow-R-Flow") in the GMC light truck line, and later, in 1966, with the Turbo-Hydramatic (THM) in GMC light trucks, whose simplified design was much less costly to manufacture. Chevrolet Division's light truck line used the less-than-adequate Powerglide all through the 1960s until Turbo-Hydramatic was made standard in 1969. Cast iron Hydramatic production ceased at Willow Run after the 1962 model year, and Controlled Coupling Hydramatic ceased in early 1964, allowing retooling time for the Turbo-Hydramatic 400, which debutted in the 1964 Cadillac models in mid-year, with Pontiac Division's Star Chief and Bonneville models being the last to use the Controlled Coupling Hydramatic (Model HM315) of any GM car. 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. This was improved upon for all 1965 models with the "D L2 L1" or "D S L" quadrant, which allowed "dual range" flexibility as did the Dual Range Hydramatic of 1953-1955. It was this version which replaced all Roto Hydramatic and Controlled Coupling Hydramatic models in GM cars in that year, ending twenty-four years of four speed automatic transmission production that obviated the need for a torque converter. Despite the name, the Turbo-Hydramatic has no mechanical or design relationship to the original Hydramatic, or the Controlled Coupling Hydramatic.

The Hydramatic was a complex design that was expensive to produce. Despite some early problems, it was reliable, and so rugged it was widely used in drag racing during the 1960s. It was not as smooth as some competitor's transmissions (notably Buick's Dynaflow), but was more efficient, especially at highway speeds. The Hydramatic paved the way for widespread acceptance of automatic shifting.

A 3-speed light-duty version of the Turbo-Hydramatic called the Turbo-Hydramatic 180 was produced by GM's Hydramatic division from 1981 to 1998 for use in a wide variety of small cars and trucks.

Hydramatic is a trade name for GM's automatic transmission division, which produces a variety of transmissions, the most notable of which is the Turbo-Hydramatic from the 1960s to the 1990s.