Common problems in vehicles with GM 4L80-E and 4L85-E transmissions include uncontrollable line rise (upward of 500 psi), high line pressure in Reverse, broken direct clutch drums and/or broken cases. These problems can be caused by excessive EPC torque signal pressure. Sonnax self-regulating boost valve kit 34200-10K eliminates these problems by limiting EPC pressure.

• Hardened steel boost valve has an encapsulated relief valve that will allow EPC pressure to exhaust if it exceeds 95-105 psi
• Boost valve with 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
• Closely toleranced sleeve restores the hydraulic integrity between the valve and sleeve
• O-Rings have been added to the sleeve to provide a positive seal that compensates for pump bore wear