September 30, 2005
In GM 4T80-E units, continuous oscillation of the converter regulator valve in the cast-aluminum bore causes bore wear which allows apply oil to leak to exhaust. Another area of concern is the valve bore end plug. The continuous movement of the regulator valve and spring causes the end plug to wiggle in the bore. This movement wears the plug and bore, resulting in balance regulated apply oil leaking to exhaust, which can prevent the converter clutch from applying and set codes.
Reconditioning the boare and installing Sonnax TCC regulator valve kit 72854-03K restores hydraulic integrity.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.