Ford E4OD and 4R100 units often display shifting irregularities which can be traced to problems with accumulator control valves. Wear ridges form as the valve moves in and out of the bore. Under high-pressure shifts, the valve is allowed to stroke too far, causing it to hang up on these ridges and block oil flow to the associated clutch. This results in soft shifts, loss of gear and burnt clutches. Sonnax 1-2 and 2-3 accumulator control valve kit 36948-13K resolves these issues and provides a firmer-than-OE shift quality.
Sonnax bore sizing tool 36948-12 (available separately) properly resizes the bore to prevent hang-up or sticking of the new valve. See instructions for details. Tool is recommended but not required.