![]() ![]() 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). A Switch Pitch can be identified outside the vehicle (with the torque converter removed) by a narrow front pump spline. 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). Many of the BOC (Buick, Oldsmobile, Cadillac) THM400s produced between 19 were equipped with a variable-pitch stator torque converter called " Switch-Pitch" (SP) these are sought after by collectors and drag racers. The following year, application expanded to Oldsmobile and Pontiac and to some full-sized Chevrolets. ![]() First introduced for the 1964 model year under the name "Turbo Hydra-Matic" in Cadillacs and "Super Turbine" in Buicks. The THM400 can be visually identified by an oil pan number four shown at General Motors Transmission Pans. Super Turbine 400 / TH400 / THM400 / THM375 / 3L80 / 3L80HD Turbo-Hydramatic 400 Transmission 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.Īlthough 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. 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. The Buick version, which followed shortly thereafter, was known as the Super-Turbine 400. In its original incarnation as the Turbo-Hydramatic 400, it was first used in the 1964 model year in Cadillacs. The Turbo-Hydramatic or Turbo Hydra-Matic (THM) series was developed to replace both the original Hydra-Matic models and the Buick Dynaflow. These transmissions mate a three-element turbine torque converter to a Simpson planetary geartrain, providing three forward speeds plus reverse. Turbo-Hydramatic or Turbo Hydra-Matic is the registered tradename for a family of automatic transmissions developed and produced by General Motors. 86), lag in getting changes to the production line notwithstanding.3-speed longitudinal automatic transmission There might be more that was done after this date.Ġ6-19-1986: New lo/rev roller clutch assembly.Ġ7-17-1986: New forward clutch assembly new pan with square magnet.ġ0-06-1986: Aux Valve Body and fluid passage changes.Ġ1-27-1987: New Aux Valve Body accumulator cover.Ġ2-09-1987: Improved reverse engagement shift feel.īut just going by the ID stamp, I'd say yours is a late '87 (model year typically starts in Sept. ![]() My notebook of references that I collected back in 1989 or 1990 show most desirable factory improvements had been done by February 1987. Probably because it's a GM Rebuild? Typical ID stamp should look like:Ī = Shift (A & B = 1st shift C & H = 2nd shift)Īs far as an early or late '87 700R4 you'd probably have to look inside and compare what you're seeing with an expert. I say "partial" ID because it doesn't look like a typical production stamping. The only meaningful thing on the tag is probably the "2CH". ![]()
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