In GM 4T80-E units, continuous oscillation of the converter regulator valve in the cast-aluminum bore causes bore wear which allows apply oil to leak to exhaust. Another area of concern is the valve bore end plug. The continuous movement of the regulator valve and spring causes the end plug to wiggle in the bore. This movement wears the plug and bore, resulting in balance regulated apply oil leaking to exhaust, which can prevent the converter clutch from applying and set codes.

Reconditioning the bore and installing Sonnax TCC regulator valve kit 72854-03K restores hydraulic integrity.

• Hardcoat anodized aluminum valve combats premature wear
• Kit re-establishes the hydraulic integrity of the valve-to-bore fit, and provides much more support for the stroking valve
• O-Ringed end plug has also been added to the kit to better seal the balance port
• Two replacement regulating springs are included in the kit so that the regulating pressure can be returned to the stock setting, or for a firmer apply with less slippage