6L80 / 6L90 High Capacity 4-5-6 Clutch Apply Piston Kit, Sonnax 104960-20K.
GM 6L80 and 6L90 transmissions often suffer failure of the 4-5-6 clutch assembly due to OE design shortcomings. Not enough clutches and insufficient clutch piston-to-plate surface area cause clutch plate failure, especially when apply pressures exceed OE specifications. The other problem is flexing and bowing of the backing plate (coning), which is a primary source of clutch failure.
Sonnax high-capacity 4-5-6 clutch apply piston kit 104960-20K features a modified OE clutch apply piston and piston dam that are used in conjunction with a specially designed toothed apply plate closest to the piston. The Sonnax toothed apply plate increases the surface area between the apply piston and first friction plate, resulting in a more even distribution of apply force to clutch plates and allowing a friction plate to run against the apply plate. This configuration eliminates the OE-waved plate. Since Powerglide-style, 45-tooth frictions are a popular 6L80/90 upgrade due to their wider friction surface, the toothed apply plate and the backing plate have a smaller inner diameter to accommodate that style. For best performance, use with Sonnax steels 104120-01 or 104120-02, BorgWarner high-energy frictions 104120-03, and Sonnax extreme duty 4-5-6 clutch hub and intermediate shaft 104680-45 (for 6L80) or 104690-45 (for 6L90).
- Solid backing plate design outperforms OE and aftermarket plates
- Toothed apply plate eliminates waved plate and allows for additional clutch capacity
- Use with Powerglide-style frictions, Sonnax steels and aftermarket, 45-tooth, 4-5-6 clutch hub