Sonnax 34200-03K Boost Valve Kit - 4L80E 4L85E

The Sonnax 34200-03K Boost Valve Kit is a high-performance replacement solution designed for GM 4L80E and 4L85E transmissions from 1991 to current. This kit addresses common transmission issues including uncontrollable line pressure rise (up to 500-600 psi), high line pressure in reverse, buzzing noises, and broken direct clutch drums or cases.

Key Features:

• Hardened steel boost valve with over 20% wider spools for superior durability and increased sealing contact area
• Annular grooves on boost valve spools reduce side-loading that causes wear
• Factory-style sleeve without external O-rings for standard applications
• Includes replacement aluminum balance oil plug with O-ring for proper sealing and pressure regulation
• Drop-in Zip Valve design for quick, hassle-free installation
• Precision-toleranced valve and sleeve restore hydraulic integrity

Problem Solved: This kit eliminates issues caused by worn boost valve sleeves that allow reverse oil leakage and worn end plugs that create pressure regulator valve imbalance. The replacement assembly ensures proper main regulator valve control and prevents torque signal circuit contamination.

Note: For applications with leakage between the sleeve and pump bore, Sonnax recommends part number 34200-01K, which includes an O-ringed sleeve to compensate for pump bore wear. Kit can be retrofitted to transmissions dating back to 1989 with included instructions.