In GM 4L60-E, 4L65-E and 4L70-E unit, severe wear of the TCC regulator valve bore is caused by oscillation of the OE valve allows regulated converter apply pressure to exhaust. This is a primary cause for TCC-related slip code P1870 and overheated converters. Exhausting apply pressure also diminishes line pressure, which can result in burnt clutches. Excess wear at the isolator valve bore reduces TCC apply pressure.

Reconditioning the bore and installing Sonnax TCC regulator and isolator valve kit 77754-03K restores normal TCC operation by shoring up the hydraulic integrity of this circuit.

• 10% Higher apply pressure
• Isolator valve lengthened to operate in unworn portions of the bore
• Sleeve manufactured from highly wear-resistant aluminum
• Hardcoat anodized aluminum valves combat premature wear
• Annular grooves help center valves in bore to reduce future side-load wear