PCV valves in Allison^® 1000/2000/2400 transmissions controls activation, release and holding pressures for the five clutches in the unit. When the PCV valves or their bores wear, the control main pressure and reverse signal pressure can cross leak and equalize, preventing proper clutch control. Additionally, wear can permit reverse signal pressure to escape to exhaust, resulting in runaway trim pressure. These conditions lead to shift issues associated with circuit pressure loss. Reconditioning the bore and installing Sonnax oversized PCV valve kit 37000-35K restores proper operation. Hardcoat annodized valve protects against premature wear.