GM TH400
Performance Transmission Upgrades

The TH400 (or Turbo 400) transmission is one of the most versatile and widely used performance transmissions in the automotive industry. From street rods and offroad desert trucks to all-out drag racing, the TH400 transmission has proven itself to be very adaptable and capable of handling massive power — not only in General Motors applications, but also adapted behind Ford, Chrysler and import engines. For builders looking to maximize performance and reliability like never before, Sonnax offers an expanding line of game-changing TH400 upgrades proven to deliver results you can trust at any power level.


The TH400 (or Turbo 400) transmission is one of the most versatile and widely used performance transmissions in the automotive industry. From street rods and offroad desert trucks to all-out drag racing, the TH400 transmission has proven itself to be very adaptable and capable of handling massive power — not only in General Motors applications, but also adapted behind Ford, Chrysler and import engines. For builders looking to maximize performance and reliability like never before, Sonnax offers an expanding line of game-changing TH400 upgrades proven to deliver results you can trust at any power level.

View Performance Parts by Application:

TH400 Build Guide

This chart breaks down the five types of Sonnax TH400 transmission parts available at different performance levels. Combine these with other Sonnax TH400 upgrades for a top-notch rebuild.

Area of Enhancement Individual Components All-In-One Upgrade
Input Shaft 1" Heavy Duty (1 Journal)
1" Heavy Duty (2 Journal)
1-1/8" Extreme Duty
Forward Drum Heavy Duty
Ideal for Any Power Level
Smart-Tech Drum Module
Ideal for Any Power Level
Direct Drum
Clutch Hub Heavy Duty Extreme Duty
Main Shaft Heavy Duty Extreme Duty

Smart-Tech® Drum Module
The Game-Changer for a Faster, Tougher, Stronger TH400

  • Increase wheel horsepower, improve acceleration, reduce shock on shifts & ramp up durability
  • All-in-one kit upgrades forward & direct drums plus everything else from intermediate sprag to back of the pump
  • Unique design improves efficiency without reducing capacity
  • Easy to install

When racing a TH400, it’s critical to upgrade the forward and direct drums. The key is not only stronger, more durable parts, but improving efficiency for better performance, consistency and safety.

Grab a radical edge over the competition with the Sonnax Smart-Tech drum module. It’s the first and only TH400 upgrade to optimize drum function with a unique configuration of both lighter and stronger components. The result: a big boost in transmission efficiency for more power to the ground and traction/stability on the shifts.

Sonnax Smart-Tech Drum Module
TH400

How It Works

Just like you might run lighter wheels, a lighter driveshaft or rotating assembly in your engine to reduce rotational mass and improve performance, you can achieve a similar effect inside your transmission with the Smart-Tech drum module.

The OE drum design limits performance.
Th400 oe drum rotating components

In a standard TH400, when the unit shifts from 1st to 2nd to 3rd, the direct drum and internal components are spinning up backwards, completely stopping and then re-accelerating to input RPM. This takes a huge amount of energy and puts a lot of strain on the transmission, which is why parts fail when they hit their limit. The traditional method of installing lighter components to improve performance won’t overcome this basic inefficiency of the TH400.

The Smart-Tech drum module gives you a better option.
Th400 smart tech drum module rotating components

Sonnax re-engineered the direct drum so only a few parts counter-rotate instead of the entire drum: the inner sprag shaft, aluminum clutch hub and friction plates. Weighing 3.3 lbs less than an aluminum drum, with weight concentrated at the center, the Smart-Tech drum module takes 68% less energy to start/stop/re-start than an aftermarket aluminum drum. This is a HUGE advantage no matter vehicle power level or what type of racing you’re looking to do.


Learn More

Watch this video to learn more about the Smart-Tech drum module, Part No. 34555-01K, or check out all the details here!


Sonnax high performance products meet the toughest challenges faced by hard-working, daily-use drivetrains as well as racing units going all-out on the street or track.

Learn About Sonnax Heavy Duty & High Performance See All Heavy Duty & High Performance Upgrades