THE TURBO 400: ENGINEERING EXCELLENCE DEFINED

The Turbo-Hydramatic 400 (TH400) is the undisputed king of GM’s classic 3-speed automatics. Introduced in the 1960s to sit behind massive big-block V8s, it is the heavy-duty big brother to the TH350 and the direct predecessor to the 4L80E. Even in bone-stock form, the TH400 is incredibly strong, but when properly modified, it is capable of handling catastrophic amounts of horsepower. Because it lacks a computer and an overdrive gear, it remains the go-to transmission for hardcore drag racers, high-horsepower street cars, and extreme off-road builds where raw, brute strength is the only requirement.

COMMON FAILURE POINTS (STOCK):

  • Intermediate Roller Clutch/Sprag (Prone to "rollover" or shattering during high-RPM 1-2 shifts)

  • Direct Clutches (Burn-up under high horsepower due to limited hydraulic apply area)

  • Forward Clutch Hub (Factory cast units can strip or break at the splines under heavy shock loads)

  • Case Lugs (Center support fretting into the aluminum case)

PERFORMANCE SOLUTIONS: While naturally strong, the TH400 needs specific hydraulic and mechanical upgrades to survive behind modern high-horsepower engines or heavy-duty drag applications. We address its few factory limits to create a bulletproof drivetrain foundation.

KEY IMPROVEMENTS:

  • Heavy-duty 34-element intermediate sprag drums to completely eliminate 1-2 shift explosion

  • Dual-feed direct clutch modifications to double the hydraulic holding force on the direct clutches

  • Billet forward clutch hubs and input shafts to withstand violent torque spikes and transbrake launches

  • Recalibrated valve bodies, full manual valve bodies, or transbrakes for instant, neck-snapping shifts

Schedule Diagnosis (Please Plan to leave Vehicle)

Turbo 400 Automatic Transmission Rebuild (TH400)

  • "th400-transmission-complete-installation-service-professional-rebuild

    TH400 | Turbo 400 Turn Key | $2,950+ Starting Price 12-24 Month Warranty

    The Flagship TH400 Performance Package Built for pure, unadulterated power. Whether you are running a blown big block, a turbo LS swap, or a heavy-duty hauler, this comprehensive, turn-key service includes professional removal, custom rebuilding, complete vehicle integration, and rigorous diagnostic testing.

    Inside the Build:

    • 34-Element Sprag Upgrade: Replaces the weak factory roller clutch with a massive 34-element sprag and upgraded drum to survive violent upshifts and high-RPM shock loads.

    • Dual-Feed Direct Modification: Hydraulically modified to apply twice the holding force to the direct clutches, preventing third-gear slip and burn-up.

    • Upgraded Forward Hub: Replaces the factory cast hub with a reinforced or billet unit to eliminate the notorious factory spline failure point.

    • Performance Converter: Heavy-duty remanufactured or custom billet torque converter built and stalled specifically for your engine's powerband.

    The Service Package Includes: Professional removal and installation. Premium synthetic fluid and all necessary build components. 12,000-mile check-up and pan inspection.

    Don't settle for a basic factory rebuild on a high-horsepower build. Our flagship TH400 Performance Package is built to take a beating. We eliminate the factory weak points and upgrade your unit with dual-fed direct clutches, a 34-element sprag, and rock-solid internal components. This is a complete, turn-key package: we handle the professional removal, custom bench build, heavy-duty torque converter pairing, and installation using premium fluids. After thorough diagnostic testing, you get a 12,000-mile pan inspection and our full 24-month/24,000-mile warranty covering all parts, fluids, and labor. Built for power, backed for peace of mind.

    Payment Notice: A 3.5% convenience fee is applied to all credit card transactions.

    TURN-KEY INSTALLATION & INTEGRATION

    Your final installation invoice will reflect the following additions where applicable: Custom Converter, High-Performance Upgrades, Premium Fluids, and applicable NC Taxes.

    AVAILABLE BUILD UPGRADES

    • OEM-Spec Torque Converter: Reliable, factory-level power transfer.

    • Heavy-Duty Sprag Drum Upgrade: Essential reliability upgrade for any V8 application making over 450HP.

    • Stage 3 Performance Package: Includes 34-Element Sprag, Dual-Feed Direct Mod, Case Saver, and a Street/Strip shift kit.

    • Stage 4 Smart-Tech Package: Includes Billet Input Shaft, Billet Forward Hub, Rollerized internals, and High-Energy clutches for maximum horsepower drag/street applications.

    • Full Manual Valve Body & Transbrake: Eliminates automatic shifting entirely for dedicated drag racing applications (Quote Required).

    PLATFORM COMPATIBILITY

    • Chevrolet: Chevelle, Camaro, Nova, C10/C20/C30 Trucks, Big Block Corvettes

    • GMC: Sierra, heavy-duty C/K series trucks

    • Pontiac: GTO, Firebird / Trans Am

    • Custom Applications: The ultimate 3-speed choice for drag racing, high-HP LS swaps, and rock bouncers.

    SHOP TECHNICAL NOTE: Unlike the TH350 (which uses a physical cable for kickdown) or the 700R4 (which uses a sensitive TV cable for internal line pressure), the TH400 utilizes an electrical kickdown switch (typically mounted on the gas pedal or carburetor linkage) for wide-open-throttle downshifts, and a Vacuum Modulator strictly to read engine load for shift timing and firmness.

    Make It