Sonnax Boost Valve Kit for GM 4L60E 4L65E 77898E-K .490 Early-Style Pump

Sonnax Boost Valve Kit for GM 4L60E and 4L65E transmissions with an early-style pump, part number 77898E-K.

This increased-ratio boost valve and sleeve assembly is designed to address internal hydraulic leakage caused by wear in the original boost circuit. The 0.490-inch valve and O-ring-style sleeve help restore hydraulic integrity and support improved line-pressure rise in the correct pump configuration.

Product Details:

• Part Number: 77898E-K

• Transmission Applications: GM 4L60E and 4L65E

• Pump Configuration: Early style

• Boost Valve Diameter: 0.490 inch

• Required Original Sleeve Length: 1.907 inches

• Design: Increased ratio with O-ring-style sealing

• Installation Type: Drop-in assembly for the matching pump configuration

Package Contents:

• One boost valve

• One boost sleeve

• Two O-rings

Fitment Requirements:

Match the original valve and sleeve configuration before ordering. This kit is an increased-ratio upgrade for the applicable early-style 0.470-inch original valve design. Transmission model or vehicle year alone does not confirm compatibility. This kit is not intended for late-style pumps using the shorter 1.809-inch sleeve.

Service Notes:

Boost valve and sleeve wear can contribute to low line-pressure rise and poor shift quality. Inspect the transmission for additional wear or damage during service; this kit does not repair previously damaged clutches or bands.

Use the vehicle-specified transmission fluid and follow the manufacturer’s installation instructions. Consider a compatible Lubegard ATF Protectant during fluid service where appropriate. Transmission fluid and protectant are not included.