March 21, 2013
GM 4T60-E and 4T65-E shift valves have changed materials over the years, starting with steel, changing to silver-colored uncoated raw aluminum, and finally anodized aluminum. These units can have a combination of these materials with the silver-colored uncoated raw aluminum being especially problematic due to scoring/scratching and intermittent sticking. Sonnax 4-3 manual downshift valve 84754-39K eliminates surface wear and reduces valve hang-up.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.