November 24, 2015
When GM 5L40-E and 5L50-E units are in Reverse gear, the Reverse lockout valve directs reverse fluid into the Reverse lockout fluid (RLO) circuit to apply the Reverse clutch and Low/Reverse clutch. Wear at the inboard spool bore can allow Reverse fluid pressure to enter the TCC signal circuit and partially stroke the TCC regulator valve. This can result in TCC overheat and loss of Reverse. The Reverse lockout valve also responds to TCC signal fluid pressure to block fluid from entering the Reverse lockout circuit, thus preventing the Reverse clutch and low/reverse clutch from applying while the vehicle is moving forward. If there is excessive bore leakage, TCC signal can cross leak into the RLO circuit, and begin to apply and burn the Reverse clutches or cause transmission damage. Sonnax Reverse lockout valve kit 55211-11K eliminates bore wear, and re-establishes the correct hydraulic pressures to prevent these problems.
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