High-mileage vehicles with a GM 400 and 425 units often experience poor line pressure control due to a worn pressure regulator bore. This will result in high cooler pressure and converter, crankshaft and/or friction element failure. This bore wear can be verified by testing line pressure and testing the pump. This hardened steel valve continuously oscillates within the cast-iron pump bore, resulting in wear. Balance line pressure is then allowed to leak past the valve and exhaust to the sump. This prevents the pressure regulator valve from moving completely to the lower line pressure position. Sonnax pressure regulator valve kit 34910-03K eliminates these problems.

• The pressure regulator valve has been modified to incorporate a solid PTFE seal ring that properly separates the balance line circuit from the pump suction, preventing cross leakage
• Kit also includes an O-ringed end plug to ensure proper back pressure to the pressure regulator valve
• This kit eliminates the need to replace the pump casting to ensure pressure control