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Turbo-Hydramatic
Turbo-Hydramatic or Turbo Hydra-Matic is the registered tradename for a family of automatic transmissions developed and produced by General Motors. These transmissions mate a three-element turbine torque converter to a Simpson planetary geartrain, providing three forward speeds plus reverse.
The Turbo-Hydramatic or Turbo Hydra-Matic (THM) series was developed to replace both the original Hydra-Matic models and the Buick Dynaflow. In its original incarnation as the Turbo-Hydramatic 400, it was first used in the 1964 model year in Cadillacs. The Buick version, which followed shortly thereafter, was known as the Super-Turbine 400. By 1973, THM units had replaced all of GM's other automatic transmissions including Chevrolet's Powerglide, Buick's Super Turbine 300, and Oldsmobile's Jetaway. Starting in the early 1980s, the Turbo-Hydramatic was gradually supplanted by four-speed automatics, some of which continue to use the "Hydramatic" trade name.
Although the Turbo Hydra-Matic name alludes to the original Hydra-Matic developed by General Motors' Cadillac division in the late 1930s, the two transmissions were not mechanically related.
The THM400 can be visually identified by an oil pan number four shown at General Motors Transmission Pans. First introduced for the 1964 model year under the name "Turbo Hydra-Matic" in Cadillacs and "Super Turbine" in Buicks. The following year, application expanded to Oldsmobile and Pontiac and to some full-sized Chevrolets.
Many of the BOC (Buick, Oldsmobile, Cadillac) THM400s produced between 1964 and 1967 were equipped with a variable-pitch stator torque converter called "Switch-Pitch" (SP); these are sought after by collectors and drag racers. A SP THM400 always has an external 2 prong connector, whereas a non-SP may have one or two (mostly one, except two on vehicles equipped with an internal pressure switch for spark timing retard). A Switch Pitch can be identified outside the vehicle (with the torque converter removed) by a narrow front pump spline. Note: GM had also used a Switch Pitch in the 1955–1963 Buick twin-turbine Dynaflow and the 1964-1967 two-speed Super Turbine 300 used in Buick and Oldsmobile (Pontiac's ST300 didn't get the SP). Vehicles originally equipped with the Switch Pitch ST300 can be identified by their "Park R N D L2 L1" gearshift selector.
THM400 units had a 32 spline output shaft. A variant known as a THM375 is a THM400 built to mate to the smaller driveshaft yokes typically used for THM350 applications. They used a Chevrolet bolt-pattern case with a longer 27 spline output shaft inside a matching tailhousing cast with a "375-THM" or "TH375" identifier. Internally, the clutch packs originally had fewer friction plates. THM375s were found in some 1971-76 Buick Lesabres and Oldsmobile Delta 88s with the 5.7 liter V-8. Somewhere in the Mid-'80s Chevrolet C10 Pickups could also come equipped with a THM375. Some "Heavy Duty" THM350s were also designated THM375-B.
Another variant is the 3L80HD, often referred to as a Turbo 475. The 3L80HD has a straight-cut planetary gear set. There is no externally visible way to determine whether the transmission contains the straight-cut planetary gear set. The THM425 front wheel drive transmission shares almost all its internal parts with the THM400. Checker Motors Corporation used the Chevrolet version of the THM400 for its "A" series taxi and Marathon models until the end of production in 1982.
By 1980, the relatively heavy THM400 was being phased out of usage in passenger cars in response to demand for improved fuel economy. The THM 400 was utilized in the C- and K-series (full-size) Chevrolet/GMC pickups and G-series (full-size) vans until 1990 when GM switched over to the 4L80E. Today, the United States Army HMMWV is the only vehicle using the THM400. The civilian Hummer H1 originally had the 3L80s, but the current model has had a 4L80E since the mid-1990s.
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Turbo-Hydramatic
Turbo-Hydramatic or Turbo Hydra-Matic is the registered tradename for a family of automatic transmissions developed and produced by General Motors. These transmissions mate a three-element turbine torque converter to a Simpson planetary geartrain, providing three forward speeds plus reverse.
The Turbo-Hydramatic or Turbo Hydra-Matic (THM) series was developed to replace both the original Hydra-Matic models and the Buick Dynaflow. In its original incarnation as the Turbo-Hydramatic 400, it was first used in the 1964 model year in Cadillacs. The Buick version, which followed shortly thereafter, was known as the Super-Turbine 400. By 1973, THM units had replaced all of GM's other automatic transmissions including Chevrolet's Powerglide, Buick's Super Turbine 300, and Oldsmobile's Jetaway. Starting in the early 1980s, the Turbo-Hydramatic was gradually supplanted by four-speed automatics, some of which continue to use the "Hydramatic" trade name.
Although the Turbo Hydra-Matic name alludes to the original Hydra-Matic developed by General Motors' Cadillac division in the late 1930s, the two transmissions were not mechanically related.
The THM400 can be visually identified by an oil pan number four shown at General Motors Transmission Pans. First introduced for the 1964 model year under the name "Turbo Hydra-Matic" in Cadillacs and "Super Turbine" in Buicks. The following year, application expanded to Oldsmobile and Pontiac and to some full-sized Chevrolets.
Many of the BOC (Buick, Oldsmobile, Cadillac) THM400s produced between 1964 and 1967 were equipped with a variable-pitch stator torque converter called "Switch-Pitch" (SP); these are sought after by collectors and drag racers. A SP THM400 always has an external 2 prong connector, whereas a non-SP may have one or two (mostly one, except two on vehicles equipped with an internal pressure switch for spark timing retard). A Switch Pitch can be identified outside the vehicle (with the torque converter removed) by a narrow front pump spline. Note: GM had also used a Switch Pitch in the 1955–1963 Buick twin-turbine Dynaflow and the 1964-1967 two-speed Super Turbine 300 used in Buick and Oldsmobile (Pontiac's ST300 didn't get the SP). Vehicles originally equipped with the Switch Pitch ST300 can be identified by their "Park R N D L2 L1" gearshift selector.
THM400 units had a 32 spline output shaft. A variant known as a THM375 is a THM400 built to mate to the smaller driveshaft yokes typically used for THM350 applications. They used a Chevrolet bolt-pattern case with a longer 27 spline output shaft inside a matching tailhousing cast with a "375-THM" or "TH375" identifier. Internally, the clutch packs originally had fewer friction plates. THM375s were found in some 1971-76 Buick Lesabres and Oldsmobile Delta 88s with the 5.7 liter V-8. Somewhere in the Mid-'80s Chevrolet C10 Pickups could also come equipped with a THM375. Some "Heavy Duty" THM350s were also designated THM375-B.
Another variant is the 3L80HD, often referred to as a Turbo 475. The 3L80HD has a straight-cut planetary gear set. There is no externally visible way to determine whether the transmission contains the straight-cut planetary gear set. The THM425 front wheel drive transmission shares almost all its internal parts with the THM400. Checker Motors Corporation used the Chevrolet version of the THM400 for its "A" series taxi and Marathon models until the end of production in 1982.
By 1980, the relatively heavy THM400 was being phased out of usage in passenger cars in response to demand for improved fuel economy. The THM 400 was utilized in the C- and K-series (full-size) Chevrolet/GMC pickups and G-series (full-size) vans until 1990 when GM switched over to the 4L80E. Today, the United States Army HMMWV is the only vehicle using the THM400. The civilian Hummer H1 originally had the 3L80s, but the current model has had a 4L80E since the mid-1990s.