GM 4T65-E Transmission Sonnax Boost Valve Kit Symptoms: Harsh Reverse Low line rise in Forward mLow line rise in Reverse Soft upshifts Cause: Bore wear near the small valve causes harsh or delayed reverse depending on the location and severity of the leak, and the temperature wear near the end plug causes soft shift quality and lowline rise. Correction: The replacement boost sleeve delivers oil 360° around the valve, reducing side load. Also the surface contact of the spools is greater, which improves durability and reduces oil loss. This Kit Includes: · Valve · Sleeve Vehicles with a 4T65-E transmission often exhibit such problems as soft upshifts (especially 1-2), delayed reverse and low line rise. This can be traced to wear of the OE boost sleeve assembly. The OE boost sleeve assembly consists of two steel valves and a steel plug that reside in the boost sleeve. The steel valves wear the aluminum sleeve and allow leakage of boost pressure. The OE boost assembly is not serviceable separately from OE, which forces the purchase of a new and expensive valve body. Sonnax offers an upgraded boost sleeve assembly 84754-30K to replace the worn OE parts and allow the OE valve body to be used and restore the hydraulic integrity of the circuit. Valves are made of hard-anodized aluminum for better wear resistance. Valves are designed to increase oil lubricity, center the valves and increase longevity. Line boost valve is longer than the OE valve to increase wear surface area. Sleeve is made of highly wear-resistant aluminum and has been designed with oil channels to evenly distribute boost valve oil. Kit is a drop-in replacement and requires no machining.