4L80E 4L85E Transmission Boost Valve O-Ring Style Sonnax 34200-01K

Common problems in vehicles with a 4L80-E transmission 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 replacement assembly 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.
• Kit includes instructions to retrofit parts dating back to 1989.