• Uncontrollable line rise
  • High line pressure
  • Broken parts
  • Broken clutch piston


Worn boost valve sleeve allows reverse oil leakage and worn end plug causes imbalance of the pressure regulator valve.


Ensure proper regulator valve control with this O-ringed balance oil plug and boost valve & sleeve kit that replaces either the 1997-later or 1996-earlier OE boost valve designs.

4L80-E, 4L85-E

Boost Valve Kit
Part No. 34200-01K

O-Ring style. Kit can be retrofit to back to '89 units. See instructions for details.

View Instructions Find a Distributor

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
  • Valve
  • Sleeve
  • Sleeve O-Rings (2)
  • Balance Plug
  • Balance Plug O-Ring
  • 4L80-E, 4L85-E Boost Valve Kit 34200-01K
  • 4L80-E, 4L85-E Boost Valve Kit 34200-01K