In Ford 4R100 and E4OD units, the holding capacity of even the largest modulator plunger valve assembly does not supply enough line pressure to the low/reverse clutch to adequately hold the clutch in diesel or heavy-duty applications. This same issue will occur in gas and street applications as the vehicle ages and wear at multiple locations continues to rob line pressure.
Sonnax heavy duty low/reverse modulator sleeve kit 36947-09K is an innovative, dual-plunger valve drop-in replacement assembly that prevents repeated low/reverse clutch distress and burn-up. The inboard, smaller plunger valve has the ratio of the larger OE plunger valve, but functions primarily as the engagement control for the low/reverse clutch. A small orifice along the valve axis prevents harsh or bang engagements by maintaining a controlled feed flow to the larger, outboard holding valve. This valve provides almost double the holding capacity to the low/reverse clutch as the OE valve.