June 06, 2018
GM 4L60-E, 4L65-E and 4L70-E transmissions often have trouble shifting into or holding 4th Gear due to excess wear in the sequence valve bore. This wear allows vital 4th servo feed and 3-4 accumulator oil to exhaust, resulting in deficient 4th servo apply pressure. Consequences are slipping or no 4th Gear operation followed closely by a burnt band.
Existing Sonnax kit 77964-04K does not address wear on the inboard two spools that is increasingly more common in these aging valve bodies. Wear at these spools can allow valuable 4th servo feed leakage, resulting in no 4th and 2-4 band wear, but can also allow leakage of 2nd clutch oil needed to apply the 2-4 band in 2nd Gear, resulting in poor 2nd Gear shifts. Leaking at the OE end plug also allows oil loss that can leave 4th Gear inoperable.
Re-establish hydraulic control and restore normal 4th Gear operation by reconditioning the entire bore and installing Sonnax oversized 4-3 sequence valve kit 77964-14K.
Kit can only be used to replace OE steel valves in bore that has not been previously reamed for 77964-04K. See chart in instructions for details.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.