4L80E 4L85E Transmission Updated Boost Valve Sonnax 34200-03K 1991 Up

Common problems in vehicles with a 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 vavle kit 34200-03K eliminates these problems.

• Hardened steel 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.
• Valve and sleeve are manufactured to close tolerances to restore proper clearance and hydraulic integrity.
• 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.