GM TH400 3-Speed Heavy-Duty Automatic · GM/Chevrolet/GMC/Cadillac/Buick · Expert rebuild service since 1987. Lifetime warranty. Free diagnostic.
1964–1991 Chevrolet/GMC trucks, Blazer, Suburban; 1964–1987 Corvette; 1964–1990 Cadillac DeVille, Fleetwood; 1964–1976 Buick Riviera; used behind 396/402/427/454 big-blocks and high-output small-blocks
| Configuration | 3-speed automatic, heavy-duty case, high torque capacity |
|---|---|
| Gear Ratios | 1st 2.48:1 · 2nd 1.48:1 · 3rd 1.00:1 · Rev 2.07:1 |
| Fluid Type | Dexron II or Dexron III ATF |
| Fluid Capacity | 11.0 qts total, 6.0 qts service refill |
The TH400 front pump supports the converter hub and its bushing wears with high-mileage use, especially in high-power applications. Front pump wear causes ATF leaks at the bellhousing and converter seal area.
Symptoms: ATF leak at front of transmission; converter whine; front seal leak
The direct clutch (3rd gear) on the TH400 is the highest-torque clutch pack. In big-block applications or with a modified converter, the direct clutches wear and eventually slip.
Symptoms: No 3rd gear or slip in 3rd; works in 1st and 2nd; RPM flare under hard acceleration
The TH400's kickdown uses an electric switch or cable. Misadjustment causes no-kickdown or constant max-pressure kickdown, wearing clutches prematurely.
Symptoms: No downshift under hard acceleration; or always harsh downshift regardless of throttle
Full disassembly. Pump bushing and front seal replaced. All clutch packs replaced with heavy-duty Alto kits. Detent cable inspected and adjusted. Valve body cleaned and rebuilt. Full Transtec soft parts kit. Converter inspected and flushed.
Dexron III every 30,000 miles. The TH400 is one of the strongest automatics ever built — with proper maintenance, it runs indefinitely. Shift kits are recommended for any performance application.
Stock: approximately 400 hp. Built with a shift kit, upgraded clutch packs, and billet input shaft: reliably handles 800+ hp. The TH400 is the go-to transmission for extreme performance builds.
The TH400 is significantly larger, heavier, and stronger. It lacks overdrive (3-speed vs the TH350's 3-speed) but handles more torque. The TH400 is the heavy-duty big-block companion; the TH350 is for small-blocks.
Excellent support — TransGo, Alto, Sonnax, and B&M all have extensive TH400 catalogs. This is the most supported vintage automatic transmission on the market.
Same transmission — 'Turbo-Hydramatic 400' is the full name, 'Turbo 400' is the common nickname, 'TH400' is the abbreviation. All refer to the same unit.
2 business days. We keep all TH400 parts in stock.
Free diagnostic, written estimate, lifetime warranty. Chicago's TH400 rebuild specialists since 1987.
