A worn OE pressure regulator valve can be detected in two ways. The first is a dynamometer test that reveals low line pressure during boost conditions (look for 50-100 psi less than specified in Reverse). The second is vehicle symptoms such as clutch slippage, reverse chatter and 3-4 clutch failure. Any of the above problems indicate bore wear that should be addressed. To address pressure regulator leakage in GM 4L60-E, 4L65-E and 4L70-E pump bodies, Sonnax offers oversized pressure regulator valve 77917-07. The Sonnax valve permits pump covers to be restored to OE specifications by correcting for wear and leakage at the pressure regulator valve. Refurbish the pump cover by reaming the bore and installing an oversized pressure regulator valve The pressure regulator valve helps restore control over the pressure regulating circuit by eliminating leakage. Note Boost valves should be checked for leakage at the same time the pressure regulator valve is being replaced.When oversizing the pressure regulator valve, it is recommended to move up one boost ratio.