Replacement front pump assembly for Ford 5R55W, 5R55S and 5R55N transmissions when line pressure falls off and engagement goes soft or delayed.
A 2002-2005 Explorer or Mountaineer that takes a long time to drop into Drive or Reverse after a hot restart, slips worse the longer it is driven, or drones with a pump whine that follows engine speed has usually lost line pressure, and on the 5R55W the source of all of it is the front pump. This is a new replacement front pump assembly for the Explorer-family 5R55W, also listed for the 5R55S and 5R55N, 2001 and up.
The pump bolts to the front of the case behind the torque converter and is turned by the converter hub. It feeds main line, which Sonnax puts at roughly 160-250 psi and up depending on demand, and supplies converter release oil that the converter regulator valve limits to 130 psi. The 5R55W's three variable force solenoids can only modulate what the pump gives them. When the gears and body wear, internal clearances open up and the pump stops holding pressure at idle and when the fluid is hot, which is why this failure is often worse after a long drive than first thing in the morning.
Two common 5R55W failures look a lot like a bad pump: wear at the intermediate and overdrive servo pin bores, which causes slipping and P0735-type ratio codes, and a worn boost valve sleeve that causes poor line rise and no Reverse. Rule both out before you pull the transmission.
Connect a gauge to the line pressure tap. Ford's 5R55W/S figures are roughly 75-120 psi in Park and Neutral at idle and 80-110 psi in the forward ranges on the 4.0L. Ford's chart for low pressure at idle in every range lists low fluid, a bad filter or filter seal, loose valve body bolts, pump or pump gasket leakage, case leakage, and a faulty valve body or separator plate. Clear the inexpensive items first. Our 5R55W pump failure symptoms guide separates flow control valve, bushing and downstream faults, and the Explorer won't move guide covers the no-movement case.
This pump is listed for the 5R55W, 5R55S and 5R55N, 2001 and up, in the Explorer, Explorer Sport Trac, Mercury Mountaineer, Mustang V6 and Lincoln LS. According to Sonnax, Explorers and Mountaineers used the W for 2002-2003 and the S from 2004, and the N in the LS and Thunderbird shares few parts with the W and S. The listing also names the Ranger, but Rangers of this era used the 4R44E/5R55E family rather than a W or S, so a Ranger owner should check our 5R55E parts. Read the transmission code on the door jamb label, compare the pump to the one coming out, or send us your year and VIN. The full lineup is on the 5R55 transmission page.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Sonnax places the W in 2002-2003 Explorers and Mountaineers and the S from 2004. Confirm with the transmission code on the driver's door jamb label. Many pump parts are shared between the two, but match the pump to yours before ordering.
Rangers of this era used the 4R44E, 4R55E, 5R44E or 5R55E, not a 5R55W. Those units take a different pump, so check our 5R55E parts or send us your VIN.
Worn pump gears and body leak more as the fluid thins with heat, so pressure drops after a long drive or a hot restart. A pressure gauge reading taken hot will show it.
Replace the front seal, pump O-ring, filter and pan gasket, and inspect the converter hub. If the clutches are burned, rebuild the transmission at the same time.
Mercon V. A 4.0L Explorer unit holds about 12.4-12.7 quarts dry. Set the final level hot through the check plug instead of filling by volume.
