Wear at the 3-4 accumulator valve and/or bore, allowing loss of torque signal, 3-4 accumulator and/or line pressure.
Refurbish the worn bore and install the Sonnax oversized valve to restore correct hydraulic clearances and shift control.
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. 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. The oversized Sonnax valves 84754-55K and 84754-58K are made from wear-resistant, hardcoat anodized aluminum to prevent wear in the refurbished bore. The spool lengths have been lengthened significantly for better hydraulic sealing and stability. Annular grooves have been added to hydraulically center the valves in the bore for wear reduction. Two valve designs exist: one for GM models and one for Volvo models.
Sonnax valve body layouts provide a detailed overview of individual units making it quick and easy to determine what’s available for the specific valve body you’re working on. See all Sonnax valve body layouts.
Contact a Sonnax Parts Distributor.
A vacuum test at torque signal, exhaust or balance ports indicated fails to hold 18" of vacuum or higher, or if visual wear is detected at these ports.