Common problems in vehicles with GM 4L80-E and 4L85-E transmissions are uncontrollable line rise (upward of 500-600 psi), high line pressure in Reverse, buzzing noise, broken direct clutch drums and/or broken cases. These problems are usually caused by reverse boost oil that enters the torque signal circuit due to a wear-created cross leak at the sleeve. High line pressure and buzz is created by oil leakage past the aluminum balance plug. The Sonnax boost valve kit 34200-01K eliminates these problems.

• Hardened steel boost valve has over 20% wider spools to provide better durability and increased sealing contact area
• Boost valve spools have annular grooves to reduce side loading that causes wear
• Quality steel boost sleeve with external O-rings provides positive seal to compensate for pump cover bore wear
• Kit includes a replacement aluminum balance oil plug with an O-ring to ensure proper sealing and adequate back pressure on the pressure regulator valve