Chevy 4T65E Transmission Sonnax TCC Apply Valve Kit Symptoms: Code 741 Converter shudder Falls out of lockup when hot High TCC slip RPM No lockup Cause: Continuous oscillation of the converter apply valve in the cast-aluminum bore causes bore wear that prevents the valve from stroking to the lock-up position. Correction: The Sonnax kit provides a positive seal to ensure proper valve stroke, and more valve support to prevent side loading that leads to wear. With PTFE seal Continuous oscillation of the converter apply valve in the cast-aluminum bore causes bore wear, particularly at the TCC signal valve spool closest to the solenoid. Wear in this area allows TCC signal oil to leak, which inhibits the valve from stroking to the lockup position. Due to the valve body casting design and oil flow, this valve is also subject to extreme side loading, which increases the wear rate. Early OE versions of this valve were made from non-anodized aluminum, and show significant wear marks. The TCC regulated apply valve should also be checked for wear. The Sonnax kit includes an O-ring to replace the OE O-ring on the TCC regulated end plug after inspection. Kit contains a hard-coat anodized aluminum valve with an expandable PTFE seal on the TCC signal valve spool to provide a positive seal to ensure proper stroking of the valve. The most inward Sonnax valve spool is almost 2.5 times longer then the OE spool, creating more valve-to-bore sealing area. Greater sealing area combined with annular grooves allows the valve to stay centered in the bore and prevents side loading. An extra PTFE seal and a new spring to fit within the valve spring pocket are included in the kit. A replacement O-ring has been included for the OE end plug, to be used after inspecting the TCC regulated apply valve. This is a drop-in replacement valve, with no machining required.