In Ford 4R100 and E4OD units, the Low/Reverse modulator plunger valve uses line pressure to control the position of the Low/Reverse modulator valve. Due to continuous oscillation of the plunger valve, wear occurs at the I.D. of the sleeve, allowing line pressure to leak to exhaust. The Low/Reverse modulator valve is prevented from properly supplying regulated line pressure to the Low/Reverse clutch, which can cause slippage, burnt clutches and loss of engine braking. Sonnax Low/Reverse modulator plunger valve kit 36947-06K renews critical clearances and restores normal clutch operation.