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  • Damaged case
  • Broken servo
  • Broken clutch piston
  • High line pressure


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 built-in relief

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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.

Kit includes instructions to retrofit parts dating back to 89.

  • Valve
  • Sleeve
  • O-Rings (2)

February 21, 2013

GM 4L80-E Vacuum Test Guide

Topics: Vacuum Testing Vacuum Test Guides Transmission GM 4L80-E Transmission

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  • 34200 10k combo
  • 34200 10k
  • 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.