Remanufactured front pump assembly for Ford 5R55S, 5R55W and 5R55N automatics. Inspected and tested; fits Explorer, Mustang, Aviator, Lincoln LS.
If your Lincoln LS, Mustang, Aviator or 2002-2008 Explorer sits in Drive for a few seconds on a cold morning before it finally grabs, or needs a stab of throttle before it will move at all, the front pump is one of the first places to look. This is a remanufactured 5R55S front pump assembly: the body, cover, gears and stator support were cleaned, inspected and tested as a complete unit, so you bolt in one assembly instead of rebuilding a worn pump piece by piece. It weighs about 13.9 lb and ships without instructions.
The converter hub drives the pump gears, and everything the 5R55S does hydraulically starts there: main line, converter charge, lube, and the feed the solenoid body uses to work the clutches and three bands. Inside the pump body sits a flow control valve that sends surplus output back to the suction side to make the pump more efficient. Sonnax documents that the OE canister and plunger in that valve wear, the plunger can stick open, and the canister O-ring relaxes so pressure bleeds away. When that happens no amount of solenoid command downstream can bring line pressure back up, which is why a worn pump looks like a whole-transmission problem.
Put a gauge on the line pressure tap before you buy anything. Ford's 5R55W/S diagnosis gives roughly 75-120 psi in Park and Neutral at idle and 80-110 psi (4.0L) or 100-135 psi (4.6L) in the forward ranges. ATSG described the cold-start version of this failure in the Lincoln LS, Jaguar, Explorer and Mountaineer as a sticking flow control valve, with the complaint worst on the first start of a cold morning. If pressure is low in every range after you have ruled out fluid level, a clogged filter and loose valve body bolts, the pump is the likely cause. Our 5R55S pump failure symptoms guide walks through separating pump wear from valve body and solenoid faults, and the harsh or delayed shifts walkthrough covers the engagement circuits behind it.
The listing covers 2002-2003 Explorer 4.0L and 4.6L, 2004-2008 Explorer and Sport Trac 4.0L, 2004-2005 Explorer 4.6L, 2005-2010 Mustang 4.0L and 4.6L, 2002-2005 Thunderbird 3.9L, 2003-2005 Aviator 4.6L, and 2000-2006 Lincoln LS and Jaguar S-Type five-speeds. Be careful at the early end of that range: Sonnax notes the 5R55N used in the 1999-2002 Lincoln LS, Thunderbird and Jaguar S-Type shares only a few parts with the W and S, and the S replaced it in those cars for 2003. If yours is a 2000-2002 LS, Thunderbird or S-Type, compare this pump to the one coming out, or send us your year and VIN before ordering. Every 5R55 part we carry is on the 5R55 collection page.
If your core is good and only the flow control valve or bushing is worn, the lower-cost 5R55S pump listing may be the better buy.
| Fits | Ford 5R55S, 5R55W, 5R55N automatic transmissions |
| Condition | Remanufactured, inspected and tested |
| Weight | 13.86 lb |
| Includes | Front pump assembly (no instructions) |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Possibly, but check first. The 1999-2002 LS used the 5R55N, which Sonnax says shares only a few parts with the 5R55W and 5R55S. Compare it with your old pump or send us your year and VIN before ordering.
That pattern points to a sticking pump flow control valve. ATSG found the valve can stick on a cold first start, and snapping the throttle open will sometimes free it. A pressure gauge on the line tap confirms it.
Mercon V. Expect about 11.2 quarts dry behind the 3.0L or 3.9L and about 12.4-12.7 quarts behind the 4.0L or 4.6L, then set the level hot through the check plug.
At minimum the front seal, pump O-ring, filter and pan gasket. Inspect the converter hub as well. If it is scored, have the converter serviced, because a damaged hub will wear out the new pump bushing.
Often the cause is the pump cover bushing, not the seal. Sonnax ties repeat front seal leaks and converter hub wear to excess hub-to-bushing clearance, so replacing just the seal will not stop the leak.
