March 21, 2013
To help control the 4th clutch apply pressure and shift feel, a 3-4 accumulator piston and an accumulator valve regulating fluid pressure are used in GM 4T65-E units. The 3-4 accumulator valve regulates line pressure using torque signal influence and directs 3-4 accumulator pressure to the spring side of the piston, controlling the 4th clutch apply. Wear at the bore or valve can allow torque signal, 3-4 accumulator or line pressures to exhaust, resulting in various 3-4 shift complaints.
Reconditioning the bore and installing Sonnax oversized 3-4 accumulator valve kit 84754-55K restores correct hydraulic clearance and shift control in GM units. For Volvo units, Sonnax offers 84754-58K.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.