In Ford 4R44E, 4R55E, 5R44E and 5R55E transmissions, both the early- and late- style EPC limit valves allow excessive high pressures which can result in harsh shifts and reverse band breakage. The early design OE EPC limit valve was positioned in the worm tracks and sealed against the separator plate. The later design OE EPC limit valve was incorporated into the end plug in the forward modulator valve bore.
Sonnax EPC limit plug kit 37947-55K features and upgraded design and will work in either of these valve body designs to reduce EPC pressure slightly to an amount that prevents high pressure in Reverse and the resultant breakage of the reverse band and reduces harsh shift complaints. An early design filter screen is included in the Sonnax kit to prevent debris from entering the EPC circuit and limit plug.