4T65E transmissions often suffer converter failure during high line pressure conditions such as max adapts or various codes due to excessive apply pressure. The torque converter piston is designed for operating pressures of 135psi but the OE apply pressure relief doesnt crack until 175 psi and can allow apply pressure to increase beyond that to over 225psi. At these high pressures the piston deflects, destroying the piston and lining. Sonnax apply relief valve 84757-01K is calibrated to crack at 135psi to prevent excess apply valve. Correctly calibrated to release pressure above 135 psi. Allows the original chain cover to be reused