Sonnax TH400 Boost Valve Kit

Improve the shift quality and firmness of your TH400 Turbo 400 transmission with this Sonnax shift kit. This kit modifies the hydraulic valve body circuits to deliver crisper, more decisive shifts that reduce clutch slippage and heat buildup. Designed for all TH400 3L80 transmissions from 1964 to 1990 in GM trucks, muscle cars, and performance vehicles.

Complete with detailed installation instructions. This shift kit is a popular upgrade during rebuilds and is essential for any performance build making serious power through the TH400. Proven to extend clutch life and improve overall transmission durability under demanding conditions.