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TH400 Level 3 - To 850 HP

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250.00 LBS
Calculated at checkout

Product Description

TH400 Level 3
Horse Power: 850
(Up to 650 ft-lbs Torque)
Converter: 10” or 11” Heavy Duty Furnace Brazed Flanged Hub with Billet Cover
Stall: 2600-4500
Master Overhaul Kit with Raybestos Generation II Racing Frictions and Hardened Kolene Steels
Transgo Re-Programming Shift Kit with Shift Command or Full Manual Forward Pattern
GEARSTAR Full Race Shift Kit
High Flow Brass Filter
New Kickdown Solenoid
Adjustable Modulator
New Kevlar Front Band
New Borg-Warner Low-Reverse Band with Heavy Duty Lugs
New Torrington Bearings
Bushing Kit with Flanged No Walk-Out Case Bushing
Thrust Washer Kit
New Low-Reverse Spring & Roller
High Capacity Direct 9-Clutch Drum with 34-Element Intermediate Sprag and Hardened Race
High-Rev Spring Kit
Heavy Duty Case Assembly
Extra Capacity Intermediate Clutch Assembly
300M Billet Forward Clutch Hub
300M Main Shaft
300M Hardened Input Shaft and Reinforced Forward Drum Assembly
High Volume High Flow Pump Assembly with New Hardened Gears
New Extra Capacity Cast Aluminum Transmission Pan with Drain Plug
New Speedometer Drive Gear
New Speedometer Driven Gear
30,000 GVW Hayden Transmission Cooler
Installation Kit: Lokar Flexible Fill Tube and Stick, Universal Transmission Mount, 
Converter Cover (Polished Aluminum)
*All transmissions include Installation Kit: Universal Fill Tube and Stick, Universal Transmission Mount, Universal Converter Cover, & ATF



The THM400 (or the Turbo 400, which it is called by drag racers and car enthusiasts) is a three-speed automatic transmission that was first introduced at the beginning of the 1964 model year in Cadillacs and Buicks (under the name Super Turbine 400). The following year, use expanded to Oldsmobile and Pontiac and to some full-sized Chevrolets (usually coupled to the Mark IV big-block V8). It can be identified by an oil pan in the shape of what some would call similar to that of the state of Texas.

Many of the Buick, Cadillac, and Oldsmobile THM400s produced between 1964-67 were equipped with a torque converter that incorporated the Switch-Pitch variable-pitch stator, which is sought after by collectors and drag racers. These can be identified outside the vehicle (with the torque converter removed) by a noticeably narrower front pump spline. Externally the switch pitch version has two electrical connections, where the non-switch pitch THM400 has only one. GM originally used a Switch Pitch torque converter in the Buick twin turbine Dynaflow transmission between 1955-1963. It was also used in the Super_Turbine_300 two speed transmissions used by Pontiac, Oldsmobile, and Buick divisions between 1964-1967. (The Super_Turbine_300 was used in 1968-1969 without the Switch Pitch torque converter.)

One variation of the THM400, known as a THM375, is simply a THM400 with a long output shaft that mates to the smaller THM350 drive shaft yoke. This can be identified by "375-THM" cast into the tailhousing. Internally the clutch packs originally had fewer friction plates. Some "Heavy Duty" THM350s were also designated THM375-B — the key to telling the difference is the shape of the pan. Another variation is the 3L80HD, which is sometimes 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. Some think units with an extra deep oil pan are 3L80HDs, but that's not a reliable indicator. The THM425 front wheel drive transmission shares almost all its internal parts with the THM400.

By 1980, usage in GM passenger cars was on a decline because of the 1973 Arab Oil Embargo, when the Hydramatic 200-4R and 700R4 overdrives were phased in. The Presidential Limo (a modified 1984 Cadillac Fleetwood Brougham) used during the Reagan Administration was the last known GM passenger vehicle to use the THM400, alongside the C- and K-series (full size) Chevrolet/GMC pickups and G-series (full size) vans ending in 1986 thereafter it was renamed to the 3L80. 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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