The Aisin Warner 55-50SN, 55-51SN transmission commonly has wear at the B4 release valve bore which can allow valuable oil pressure to leak, or cause the valve to stick in the bore. Either results in various 2-3 and 3-2 shift complaints, and can result in a burnt 3rd Gear band. This valve is reacted on by solenoid modulator and 4-5 clutch feed pressures to control the release of the B4 (3rd Gear) band. When the bore is worn, release pressure and/or solenoid modulator pressure can exhaust, resulting in shift complaints. Sonnax oversized B4 release valve kit 59947-26K restores hydraulic integrity to the bore and eliminates wear related complaints and sticking valves. The inboard valve spool has been made considerably longer than the OE design to add greater stability and sealing capability to the valve/bore interface.
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.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.