TH400 Transmission for Sale | OEM GM Turbo Hydra-Matic 400 3-Speed Automatic

Description

Transmission Background

The TH400, formally the Turbo Hydra-Matic 400, is the heavy-duty 3-speed automatic produced by General Motors from 1964 through 1990. It is one of the most successful and respected automatic transmissions ever built, used in millions of GM cars and trucks across the small-block, big-block, Cadillac V8, Pontiac V8, Buick V8, and Oldsmobile V8 families. Beyond GM, the TH400 was licensed to Rolls-Royce, Jaguar, Ferrari (in the 400 and 412), the United States Army HMMWV, and many other manufacturers, a testament to its bulletproof reliability and ease of integration.

The TH400 architecture uses a Simpson planetary gear set with 1st at 2.48:1, 2nd at 1.48:1, 3rd direct at 1.00:1, and reverse at 2.08:1. The case is cast aluminum alloy with the bell housing integrated into the case casting. The conservative factory rating is 450 lb-ft of input torque, but built TH400s with hardened internals, manual valve bodies, and trans-brakes routinely handle 3,000-plus horsepower in pro mod drag racing. The TH400 is the dominant heavy-duty 3-speed automatic in drag racing and remains a popular choice for muscle car restoration and restomod projects.

The TH400 was renamed the 3L80 in 1990 (3-speed, Longitudinal, 8,000 lb GVWR) under GM’s new naming convention. It was phased out at the end of 1990 and replaced by the electronically controlled 4-speed 4L80E in 1991. However, the TH400 architecture lived on for decades in performance and racing applications, with companies like ATI, Coan, Jake’s Performance, and Reid Racing producing race-built TH400s for serious applications.

A documented used OEM TH400 with verified bell housing, tail housing length, donor vehicle, and configuration is the right transmission for any classic GM muscle car, classic GM truck, off-road build, or hot rod project. We document the tail housing length, bell housing pattern (always BOP for direct GM fit), 2WD or 4WD configuration, and donor vehicle on every order before shipping.

When Replacement Becomes Necessary

• Slipping in 1st or 2nd gear, indicating clutch pack or band wear
• Hard or delayed engagement when shifting into drive or reverse
• No reverse, often the rear band
• Burnt fluid (dark, acrid odor)
• Limp behavior with the transmission stuck in 2nd or 3rd
• Pump whine on takeoff, common on neglected high-mileage units
• Cracked case, rare on aluminum but possible from impact
• Worn output shaft splines or yoke wear
• Kickdown switch failure causing improper downshift behavior

What to Know Before You Buy

• Bell housing pattern matters: TH400 uses the BOP (Buick-Olds-Pontiac) bell housing pattern, which is compatible with ALL GM V8 engines (small block Chevy, big block Chevy, Pontiac, Buick, Olds, Cadillac). It is NOT directly compatible with Ford or Chrysler engines. Adapters from Bendtsen, Wilcap, and others exist for Ford and Mopar applications.
• Tail housing length matters: TH400s came with three primary tail housing lengths. Short (4 inches, typical passenger car), medium (6 inches, typical truck and Suburban), and long (9-plus inches, RV and motorhome). Wrong tail housing length puts your driveshaft yoke in the wrong position. We confirm tail housing length on every order.
• 2WD versus 4WD: 4WD TH400s use a transfer case adapter for the NP203, NP205, or BorgWarner 1345. The case is the same; the tail housing changes.
• Yoke and slip yoke: most 2WD TH400s use a 32-spline slip yoke output. Some heavy-duty applications use a fixed-yoke configuration. Match to your driveshaft setup.
• Fluid: TH400 takes Dexron II or III. Some performance shift kit applications recommend Type F for firmer shifts. We flag fluid recommendations on every order.

TH400 Variants by Application

Critical buyer information for ordering the correct TH400:

What Ships and What Does Not

Direct-Fit Vehicle Applications

Non-GM Adapter Applications

For Ford, Mopar, AMC, and Jeep applications requiring a TH400, Bendtsen, Wilcap, Advance Adapters, and Novak Conversions offer adapter plates. Call us to discuss your specific build.

Search Terms Buyers Use

Used OEM Versus Professional Rebuild

For a classic GM muscle car, classic GM truck, or hot rod project on a reasonable budget, a documented used TH400 with bell housing verified and gears cycled is the cost-effective path. For a high-horsepower performance build or a serious drag race application, a professional rebuild with hardened internals, a manual valve body, and a high-stall torque converter is the better investment. Rebuilt performance TH400s typically run $2,500 to $5,000 from established GM transmission shops, plus the torque converter and converter cooler.

Inspection Workflow

• Test stand pressure and shift testing across all 3 forward gears and reverse
• Bell housing pattern verified: BOP (all GM V8) confirmed
• Tail housing length measured: short (4 inch), medium (6 inch), or long (9-plus inch)
• 2WD versus 4WD output configuration documented
• Donor vehicle identified from external indicators where available
• External seal and gasket inspection at pan, tailshaft, and pump
• Output shaft and yoke condition assessed

Pre-Purchase Buyer Notes

• Verify tail housing length against your driveshaft setup: short for most passenger cars, medium for trucks, long for RVs. Wrong length puts the yoke out of position.
• Match 2WD or 4WD: 4WD adapters mount to NP203, NP205, or BW 1345 transfer cases. Wrong adapter creates driveshaft mismatch.
• BOP bell housing is universal for GM V8: works with all GM V8 families (SBC, BBC, Pontiac, Buick, Olds, Cadillac). For Ford or Mopar applications, plan an adapter plate purchase.
• Plan a shift kit at install: TransGo and B&M shift kits firm up shifts and extend clutch life. Inexpensive insurance.
• Use the correct fluid: Dexron II or III for stock applications. Type F for some performance shift kit applications. Match the kit manufacturer recommendation.

Why Buy From Part Nests

• Tail housing length confirmed: short, medium, or long documented before payment
• BOP bell housing verified for all GM V8 direct fit
• 2WD versus 4WD output configuration noted on every order
• Donor vehicle disclosed where identifiable
• All 3 forward gears and reverse pressure and shift tested before shipment
• No core return required
• Free freight pallet delivery to every state
• 15 day replacement warranty against internal defects
• Call us to speak with someone who knows TH400 tail housing variations, BOP bell housing GM V8 compatibility, and adapter options for non-GM applications