Sonnax Transmission Company has introduced a new aluminum clutch steel for GM TH400 transmissions to help racers maximize drivetrain efficiency and responsiveness. The lightweight plate reduces forward clutch pack weight by approximately one pound for improved performance.
For racers chasing every possible performance advantage, optimizing the TH400 forward/direct drum system is critical. Traditional clutch packs use steel separator plates, but the Sonnax aluminum clutch steel is approximately 63% lighter at only 1.6 ounces. The significant weight reduction decreases clutch rotational mass, improving drum efficiency and acceleration without sacrificing durability. The plates feature a custom, 28-tooth design for use with Sonnax 28-spline forward drums, including the Smart-Tech® drum module.
Key Features
- Improves acceleration and rotating efficiency of Sonnax 28-spline forward drums
- 63% Lighter aluminum plates reduce forward clutch pack weight by about 1 lb.
- Anodized plates will not wear or discolor fluid
- A lightweight spacer option behind standard steel plates when reducing forward or direct clutch friction count
The new aluminum clutch steel (Part No. 34555-44A) is available now through authorized distributors. Learn more about this and other Sonnax performance transmission upgrades at www.sonnax.com.
This story was originally published on September 18, 2026. 
