TH400 Transmission

When strength, simplicity, and proven performance matter, the TH400 transmission remains one of the most respected automatic transmission options. Originally introduced by General Motors in the 1960s, the Turbo 400 transmission quickly earned a reputation for handling serious horsepower and torque in everything from muscle cars and drag cars to heavy-duty trucks.

Today, the TH400 remains a top choice for street performance builds, hot rods, drag-racing applications, and high-horsepower custom vehicles. Its rugged design, extensive aftermarket support, and ability to withstand extreme power levels have made it a staple in the performance automotive world for decades.

TH400 Transmission Basics

The TH400 transmission, often referred to as the Turbo 400 transmission, is a three-speed automatic transmission known for its exceptional durability and torque capacity. Designed for high-performance and heavy-duty applications, the TH400 became standard equipment in many GM muscle cars, trucks, and full-size vehicles.

One of the reasons the Turbo 400 remains popular is its ability to handle substantial power while maintaining reliability. Unlike many modern transmissions that rely heavily on electronics, the TH400 utilizes a robust hydraulic design that has proven itself under some of the most demanding conditions imaginable.

Why Performance Enthusiasts Choose the Turbo 400 Transmission

The Turbo 400 transmission has survived decades of technological advancements because it simply works. Builders and enthusiasts continue to rely on it because of its reputation for strength and consistency.

Some of the biggest advantages of the TH400 include:

Exceptional Strength

The TH400 was designed to handle significantly more torque than many other automatic transmissions of its era. With the right internal upgrades, it can support horsepower levels that far exceed its original factory ratings.

Proven Racing Performance

From drag strips to street/strip applications, the Turbo 400 transmission has become a go-to choice for racers who demand consistent performance under extreme conditions.

Simple, Reliable Design

The hydraulic operation of the TH400 eliminates many of the complexities found in modern electronically controlled transmissions. This simplicity contributes to long-term reliability and easier servicing.

Extensive Upgrade Potential

The aftermarket support available for the TH400 transmission allows builders to tailor the transmission to virtually any horsepower level, vehicle weight, tire size, rear gear ratio, and intended use.

TH400 Transmission Performance Levels

Gearstar offers several TH400 transmission options to match your horsepower, torque, and driving goals.

TH400 Level 1

Ideal for street-driven vehicles.

Power Rating:

• Up to 400 HP

• Up to 400 ft-lbs

Features a custom torque converter, upgraded friction materials, TransGo shift kit, high-flow pump, and key durability upgrades.

TH400 Level 2

Built for higher-powered street applications.

Power Rating:

• Up to 550 HP

• Up to 500 ft-lbs

Includes additional internal upgrades for increased strength while maintaining excellent drivability.

TH400 Level 3

Designed for serious street and street/strip builds.

Power Rating:

• Up to 800 HP

• Up to 750 ft-lbs

Features racing frictions, increased clutch capacity, upgraded sprag components, and a billet Yank performance converter.

TH400 Level 4

For high-horsepower street and racing applications.

Power Rating:

• Up to 1,200 HP

• Up to 1,000 ft-lbs

Includes 300M billet components, upgraded clutch assemblies, Kevlar band, and extensive internal reinforcements.

TH400 Level 5

Our most extreme TH400 transmission for sale.

Power Rating:

• Up to 2,000 HP

• Up to 2,000 ft-lbs

Built for serious racing with a Reid Racing SFI-certified case, bellhousing, and maximum-strength internal components.

TH400 4x4 Transmission Options

We also offer Turbo 400 transmission packages for high-performance 4x4 applications.

TH400 4x4 Level 3

Power Rating:

• Up to 800 HP

• Up to 700 ft-lbs

Designed for off-road, towing, and performance truck applications requiring exceptional durability.

TH400 4x4 Level 4

Power Rating:

• Up to 1,000 HP

• Up to 900 ft-lbs

Features many of the same high-strength upgrades found in our performance TH400 builds, optimized for demanding four-wheel-drive use.

TH400 Transmission FAQs

Is a TH400 a 3 Speed or 4 Speed?

The TH400 transmission is a 3-speed automatic transmission with gear ratios of 2.48:1, 1.48:1, and 1.00:1. It does not have an overdrive gear, which contributes to its simple, durable design.

How Much HP Is a TH400 Rated For?

A TH400 transmission can support a wide range of horsepower depending on its build. Gearstar's TH400 lineup ranges from 400 horsepower in Level 1 applications to 2,000 horsepower in Level 5 race-ready builds.

What's the Difference Between a 350 and a 400 Transmission?

The TH400 is generally stronger than the TH350. It features larger internal components and greater torque capacity, making it a popular choice for high-performance, racing, towing, and heavy-duty applications.

Is Turbo 400 Better Than 4L80E?

It depends on the application. The Turbo 400 transmission is known for its simplicity, strength, and reliability in performance builds. The 4L80E offers similar strength but adds an overdrive gear, making it better suited for highway driving and lower cruising RPM.

The Gearstar Difference

Since 2001, Gearstar Performance Transmissions has specialized in delivering custom-built transmission and torque converter packages for hot rods, muscle cars, custom builds, cruisers, performance street cars, and heavy-duty applications.

Every TH400 transmission for sale from Gearstar undergoes a detailed build process designed to ensure quality, consistency, and performance.

One Builder, One Transmission

Unlike assembly-line production facilities, Gearstar assigns one experienced builder to each transmission. That builder handles the entire build from start to finish, ensuring complete accountability and attention to detail throughout the process.

Complete Tear-Down and Inspection

Every transmission core is completely disassembled and thoroughly cleaned in an industrial parts washer. The case is then media blasted to expose the raw aluminum surface.

This process allows our team to carefully inspect every case for cracks, structural defects, wear issues, and other potential reliability concerns. 

Built Specifically for Your Application

No two vehicles are exactly alike. That's why every Turbo 400 transmission we build is customized around your specific combination.

We consider factors such as vehicle weight, engine horsepower and torque, rear gear ratio, tire size, intended use, and your desired driving characteristics

This allows us to properly configure both the transmission and torque converter to work together as a complete package.

Dyno Tested Before Shipment

Once assembly is complete, the transmission and torque converter are tested together on one of Gearstar's in-house transmission dynos.

Every Gearstar-built transmission undergoes a complete dyno validation process, including 100 miles of simulated testing before shipment. 

Get a Custom TH400 Transmission Quote

Choosing the right TH400 transmission involves more than selecting a horsepower rating. Vehicle weight, tire size, rear gearing, engine characteristics, and intended use all play important roles in determining the ideal transmission and torque converter combination.

If you're looking for a Turbo 400 transmission built specifically for your application, contact Gearstar today. Our team can help you select the right build level and create a custom transmission package engineered for your vehicle, performance goals, and driving style.