4L80E, 4L85E

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

Symptoms:

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

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

Correction:
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.

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.

Note:
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.

Contents:

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

SONNAX Installation Instructions