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


Unregulated EPC pressure forces pressure regulator into high line position.


This self-regulating reverse boost valve regulates EPC pressure to 95-105 psi with an encapsulated relief valve.

4L80-E, 4L85-E

Boost Valve Kit
Part No. 34200-10K

With encapsulated relief valve.

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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
  • Valve
  • Sleeve
  • O-Rings (2)

  • 4L80-E, 4L85-E Boost Valve Kit 34200-10K
  • 4L80-E, 4L85-E Boost Valve Kit 34200-10K
  • 4L80-E, 4L85-E Boost Valve Kit 34200-10K details

You need this if...

Wet Air Test can be done using either the reverse boost orifice or the torque signal orifice for this particular application.