4L80E 4L85E Transmission Sonnax Boost Valve Kit 34200-10K Common problems in vehicles with a 4L80-E transmission 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. The Sonnax self-regulating reverse boost valve 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. Note Kit includes instructions to retrofit parts dating back to 89. Contents Valve Sleeve O-Rings (2)