sonnax-black Facebook-color LinkedIn-color maillink printlink r_and_r_only SERVOFIX-logo-web Twitter-color VBFIX-logo-web video-logo-web warranty_only Youtube-color


  • Broken parts
  • Buzzing noise
  • Uncontrollable line rise
  • High line pressure


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


Ensure proper main regulator valve control with this boost valve and sleeve kit with O-ringed balance oil plug. Replaces '91 current OE boost valves.

4L80-E, 4L85-E

Boost Valve Kit
Part No. 34200-03K

Fits '91-later units with factory-style sleeve. Can be retrofit to '89-91 units. See instructions for details.

You need this if... View Instructions

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.

If you detect leakage between the sleeve and pump bore, use 34200-01K, which includes an O-ringed sleeve to compensate for pump bore wear and prevent pump scrappage.

  • Balance Plug with O-Ring
  • Boost Sleeve Factory style, no O-rings
  • Boost Valve

February 21, 2013

GM 4L80-E Vacuum Test Guide

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

Read Now
  • 34200 03k combo
  • 34200 03k

You need this if...

Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.

  • 34200 03k test