Vehicles with listed GM transmissions may exhibit insufficient line rise in drive ranges, soft shifts and/or burnt clutches. These problems may be caused by continuous oscillation of the boost valve within the boost sleeve, creating excessive wear and a path for EPC fluid pressure to leak to exhaust. Sonnax boost valve kit 104520-12K has upgraded materials and minimal clearances to prevent wear and restore proper hydraulic control. The sleeve also has a slightly larger EPC feed orifice to provide quicker throttle response. A new pressure regulator valve outer spring is also included to replace weakened original springs and provides a modest 5 psi increase across the pressure curve.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.