Required reamer 77968-RM is no longer in production. Check with your distributor for availability.
A low throttle boost condition is a common complaint in vehicles with a vehicles with GM 4L60 transmissions. This loss of throttle boost oil creates poor line rise and accelerates 3-4 clutch and band failure. In late-model transmissions, the hardened steel throttle valve continuously oscillates in the cast iron valve body bore and eventually wears the three bore diameters. This wear allows throttle valve feed oil to leak past the valve spool and exhaust, resulting in a low throttle boost condition. This excessive leakage can be eliminated by reconditioning the bore and installing Sonnax oversized throttle valve 77968.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.