According to Sonnax, this drum module is designed to correct a specific flaw of the TH400: the fact that the direct drum counter rotates, spinning backwards in first gear, brakes to a complete stop on the 1-2 shift, then goes from 0 RPM to input RPM on the 2-3 shift. Significant energy is wasted through this cycle that robs power, upsets traction on the shifts and contributes to broken internal parts, the company says.
Sonnax says that compared to aluminum direct drums, the Smart-Tech drum module (part no. 34555-01K) reduces the weight of the counter-rotating components by 3.3 lbs. Additionally, because the weight of the Sonnax counter-rotating parts is closer to the centerline, there is a 68% reduction in energy required to stop and restart during the 1-2 and 2-3 shifts. The benefits are increased wheel horsepower, better acceleration, less shock on the shifts and improved durability.
Additional details on the drum module include:
- Complete kit replaces both forward and direct drums and includes everything from intermediate sprag to the pump; a selection of Sonnax input shafts is available separately;
- 100% new content, no used core pieces;
- Includes larger-diameter, 36-element sprag and sprag race that works with OE intermediate clutches;
- Includes six-friction forward clutch pack and seven-friction direct clutch pack.