Description
About This Transmission
The TH400, formally the Turbo Hydra-Matic 400, is the heavy duty 3 speed automatic transmission 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 gear 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 GMs 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, Jakes 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.
Signs You Need a Replacement Transmission
- 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, smells acrid)
- Limp behavior, transmission stuck in 2nd or 3rd gear
- 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
- Kick-down switch failure causing improper downshift behavior
Known Things 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 are widely available for Ford and Mopar swaps.
- Three tail housing lengths: TH400 came with short (passenger car), medium (intermediate), and long (pickup and SUV) tail housings. Tail housing length affects driveshaft length and transfer case adapter on 4WD applications. We confirm tail housing length on every order.
- 2WD vs 4WD: 4WD TH400s have a transfer case adapter on the rear of the case for the NP203, NP205, BorgWarner 1345, or other GM transfer cases. The case itself is the same; the tail end changes. Common in K series Chevy/GMC trucks and SUVs.
- TH400 vs 4L80E: The 4L80E is the electronic 4 speed evolution of the TH400. They share architecture but the 4L80E has an overdrive 4th gear, electronic shift control, and a lockup torque converter. They are not direct swaps without ECU and harness work.
- TH475 heavy duty: The TH475 is a heavy duty variant of the TH400 used in 1970s heavy duty pickups. It uses similar architecture with stronger internals.
- TH375 light duty: The TH375 is a lighter duty variant used in 1970s low horsepower applications. It has a TH350 driveshaft yoke spline. Avoid TH375 if you need TH400 strength.
- Variable pitch stator (1965 to 1967 only): Early Buick and Cadillac TH400s used a variable pitch stator with a double plug. This is a rare and collectible variant.
- Kick-down switch: TH400 uses an electrical kick-down switch on the throttle linkage. TH350 uses a mechanical cable. The TH400 will have an electrical plug on the side of the case.
TH400 Variants and Tail Housing Configurations
Verified configurations:
| Variant | Years | Application | Notes |
|---|---|---|---|
| Standard TH400 (passenger car) | 1964 to 1986 | Cadillac, Buick, Olds, Pontiac, Chevy passenger cars | Most common variant. Short to medium tail. |
| TH400 truck (long tail) | 1968 to 1990 | C/K series pickup, Suburban, GMC trucks | Long tail housing for truck driveshaft length. |
| 4WD TH400 | 1969 to 1990 | K series 4WD pickup, K5 Blazer, Jimmy | Transfer case adapter for NP203, NP205, BW1345. |
| TH475 (heavy duty) | 1972 onward | 3/4 ton and 1 ton heavy duty trucks | Stronger internals. TH475 designation on tail. |
| TH375 (light duty) | 1972 onward | Light duty cars with TH350 driveshaft | AVOID for TH400 strength applications. TH350 spline output. |
| Variable pitch stator | 1965 to 1967 | Buick and Cadillac | Rare collectible. Double plug stator. |
| 3L80 (renamed) | 1990 | Late C/K trucks and vans | Same as TH400. Just renamed. |
| The standard TH400 with the BOP bell housing pattern fits all GM V8 engines. For non-GM applications (Ford, Chrysler), an adapter plate is required. Bendtsen, Wilcap, and others sell suitable adapters. Call (240) 301-0095 for fitment guidance. |
|---|
What Is Included, What Is Not Included
| INCLUDED | Complete transmission case (with integrated BOP bell housing), gear sets, valve body, torque converter, internal harness as applicable, output shaft, tail housing as configured. |
|---|---|
| NOT INCLUDED | Flexplate or flywheel (engine specific), transmission cooler lines, fluid, transfer case (4WD applications), drive shaft, dipstick and tube, kick-down switch wiring (sometimes). |
| Adapter for Ford / Mopar | Not included. Available from Bendtsen, Wilcap, and others. |
| Core Note | No core charge. You are not required to return your old transmission. |
Vehicle Compatibility, Direct Fit
Direct factory applications (all GM passenger cars and trucks with V8 engines):
| Chevrolet Camaro | 1967 to 1981 (with V8 options) |
|---|---|
| Chevrolet Chevelle / Malibu | 1965 to 1972 |
| Chevrolet Corvette | 1965 to 1981 (heavy duty option) |
| Chevrolet Impala / Caprice | 1965 to 1980 (V8) |
| Chevrolet Suburban | 1968 to 1990 |
| Chevrolet C/K Series Trucks (C10, C20, C30) | 1968 to 1990 |
| Chevrolet K5 Blazer | 1969 to 1990 |
| GMC Sierra / Jimmy / Suburban | 1968 to 1990 |
| Pontiac Firebird / Trans Am | 1967 to 1981 |
| Pontiac GTO | 1965 to 1972 |
| Pontiac Grand Prix / LeMans | 1965 to 1976 |
| Buick Skylark / Riviera / GS | 1965 to 1976 |
| Buick Grand National (rare) | 1984 to 1987 |
| Oldsmobile Cutlass / 442 / 88 / 98 | 1965 to 1976 |
| Cadillac Eldorado / Fleetwood / DeVille / Brougham | 1964 to 1980 |
| Hummer H1 (early) | 1992 to 1995 (replaced by 4L80E mid-1990s) |
Adapter-Required Applications (NOT direct fit)
TH400 uses BOP bell housing pattern. The following engines require an adapter plate from Bendtsen, Wilcap, or similar to bolt to a TH400:
| Ford Windsor V8 (289, 302, 351W) | Adapter plate required |
|---|---|
| Ford Cleveland V8 (351C, 351M, 400) | Adapter plate required |
| Ford FE V8 (390, 427, 428) | Adapter plate required |
| Ford 385 series V8 (429, 460) | Adapter plate required |
| Chrysler LA V8 (318, 340, 360) | Adapter plate required |
| Chrysler B/RB V8 (383, 440) | Adapter plate required |
| AMC V8 (304, 360, 401) | AMC factory adapter or aftermarket |
| Jeep applications | Novak, Advance Adapters offer Jeep specific kits |
Direct engine compatibility (BOP bell housing pattern, no adapter needed): Chevrolet small block V8 (262, 265, 283, 305, 327, 350, 400). Chevrolet big block V8 (396, 402, 427, 454). Pontiac V8 (326, 350, 389, 400, 421, 428, 455). Buick V8 (215, 300, 340, 350, 400, 430, 455). Oldsmobile V8 (260, 307, 330, 350, 400, 425, 455). Cadillac V8 (368, 425, 472, 500, 4.1, 4.5, 4.9, 5.7).
Not sure if this fits? Call (240) 301-0095 with your year, model, and engine. We confirm bell housing pattern and tail housing length before every order ships. We can also help guide you on adapter plate options for Ford or Chrysler swap projects.
Common Names and Search Terms
| TH400 | Most common technical search |
|---|---|
| Turbo 400 | Common nickname |
| Turbo Hydramatic 400 | Full name |
| THM400 | Alternative abbreviation |
| GM 3 speed automatic | Architecture search |
| Chevy TH400 | Chevrolet specific search |
| 3L80 | Post-1990 name |
| Heavy duty GM auto | Class search |
| Camaro TH400 | Camaro restoration |
| C10 TH400 | C10 truck search |
Used OEM vs Rebuilt vs Race Built TH400
A documented used OEM TH400 is the most cost effective option for any classic GM muscle car, classic truck, or restomod project. Pricing is roughly half of a rebuilt unit. Our TH400s are pressure tested, shift tested, and the tail housing length, bell housing, and donor vehicle are documented.
A professionally rebuilt TH400 from a specialty shop typically runs $1,800 to $3,200 for a street build. This includes new clutches, bands, gaskets, and a re-manufactured torque converter. This is the right path for high mileage classic restorations.
A race built TH400 with trans-brake, manual valve body, hardened input, billet drum, and high stall torque converter typically runs $5,500 to $12,000 plus depending on power target. Race TH400s from ATI, Coan, Jakes Performance, and Reid Racing routinely handle 1,500 to 3,000 plus horsepower in pro mod and outlaw drag racing.
Condition and Inspection Process
- Pressure test on the dyno bench, line pressure recorded across all gears
- Shift test on the dyno bench, all 3 forward gears, reverse, and lockup tested
- Torque converter inspected for shudder material
- Valve body inspected and pressure tested
- Internal bands and clutch packs inspected where accessible
- Case inspected for cracks, output shaft for runout, splines for wear
- Bell housing pattern confirmed (BOP, GM V8 direct fit)
- Tail housing length documented (short, medium, or long)
- 2WD or 4WD configuration documented
- Donor vehicle and verified mileage where available
Mileage on a classic TH400 is rarely a meaningful number because most have been pulled from cars with multiple speedometer cables or engines. We document what we know and disclose unknowns clearly.
Buyer Tips, What to Know Before You Order
- Bell housing first: TH400 uses BOP bell housing. Direct fit on all GM V8s. Adapter required for Ford or Chrysler.
- Tail housing length matters for driveshaft length. Short tail (passenger car), medium (intermediate), long (truck). Match to your application.
- 2WD vs 4WD: Confirm before ordering. 4WD has transfer case adapter on the tail.
- Plan a fresh fluid (Dexron III or VI), filter, and pan gasket at install regardless of unit condition.
- Consider a shift kit (TransGo, B&M) at install for crisper shifts and longer life on a daily driver classic.
- For racing: Plan a manual valve body, trans-brake, and high stall torque converter. Stock TH400 valve body is calibrated for street duty.
- Ford or Chrysler swap: Order the BOP TH400 unit AND a quality adapter plate from Bendtsen or Wilcap in parallel.
- Cooler matters: Any TH400 in a tow vehicle, drag car, or off-road build should have an auxiliary transmission cooler.
Why Buy From Vaz Auto Solutions
- BOP bell housing pattern verified (direct fit on all GM V8s)
- Tail housing length documented (short, medium, or long)
- Donor vehicle disclosed (Camaro, Chevelle, C10, etc.)
- 2WD or 4WD configuration confirmed before shipping
- Pressure tested and shift tested on the dyno bench
- Variant identified (standard, TH475 heavy duty, or 4WD)
- Adapter guidance for Ford or Mopar swap projects
- No core charge, keep your old transmission
- Free freight pallet delivery to all 50 states, no hidden fees
- 15 day replacement warranty on internal defects
- Call (240) 301-0095, talk to someone who actually understands the BOP bell housing pattern, the TH400 vs TH475 distinction, and the adapter options for non-GM swaps
Tony (verified owner) –
I snagged a TH400 from Find Auto Parts Online for my ’69 Camaro resto-mod. This tranny’s a beast! Shifts smooth, handles the 500 horses from my small block Chevy like a champ. Couldn’t be happier with the purchase!
Jenny (verified owner) –
Found a great deal on a TH400 at Find Auto Parts Online for my ’78 Silverado project. Solid build, shifts crisp, perfect for towing and off-road adventures. Definitely recommend if you’re looking for reliability and performance.
Tony C., Detroit MI –
Bought a TH400 from Vaz for my 1969 Camaro 502 big block restomod. They confirmed BOP bell housing for my Chevy big block, medium tail housing for my passenger car driveshaft, and the unit pulled from a 1972 Camaro SS donor. Pressure tested before shipping. Bolted right up. Tranny handles the 600+ horsepower from my 502 like a champ. Clean firm shifts.
Jenny M., Salt Lake City UT –
Replaced the 4WD TH400 in my 1978 K10 Blazer with one from Vaz. They confirmed long tail with NP205 transfer case adapter, came out of a 1979 K20 truck. Pressure tested, shift tested, bell housing confirmed BOP. Half star off because shipping took 11 business days but the transmission is solid. Pulling my 8,000 lb camper without issues.