Complete front pump assembly for the Ford 5R55W, 5R55S and 5R55N five-speed in 2001-up Explorer, Mountaineer, Mustang and Lincoln LS.
If your Explorer, Mountaineer, Mustang V6 or Lincoln LS keeps puddling fluid at the bell housing no matter how many front seals go in, or it has started to sit for a second before it grabs Drive, the front pump is the part to look at. This is a complete front pump assembly for the Ford 5R55 five-speed family - 5R55W, 5R55S and 5R55N, 2001 and later - so the body, gears, cover and bushing all come as one unit instead of reusing a housing that already has wear in it. Shipping weight is about 13.2 lb.
The pump is driven by the torque converter hub and makes all of the line pressure the transmission runs on. On the 5R55 family it does two more jobs that matter for diagnosis. First, it carries a flow control valve that dumps excess pressure back to the suction side to save pump effort; Sonnax notes that valve's plunger commonly sticks open or its canister wears, which drops line pressure. Second, the pump cover carries the bushing the converter hub rides in. That bushing is a finish-in-place part from the factory, and Sonnax ties excessive hub-to-bushing clearance in soft babbitt bushings to repeat front seal leaks and a worn converter hub. A whole assembly replaces both wear points at once.
Put a gauge on a line pressure tap before condemning anything. ATSG documented the cold-start version of this failure: a groove wears in the flow control sleeve, the valve lodges open on startup, and pressure reads 40 psi or lower until a snap of the throttle sometimes frees it. A leak that wets the bell housing should be traced too, because the 5R55 also leaks from the pan, cooler lines and case connector; our 5R55 fluid leak guide covers where to look. If the complaint is delayed engagement, read the 5R55W pump failure symptoms guide first, since a stuck servo or valve body can produce the same delay with a healthy pump.
This assembly is listed for the 5R55W, 5R55S and 5R55N, 2001 and up: Explorer, Explorer Sport Trac and Mercury Mountaineer, the 2005-2010 Mustang V6, and the Lincoln LS. Per Sonnax, the W was in the 2002-2003 Explorer and Mountaineer, the S replaced it for 2004-2005, and the N ran in the Lincoln LS and Thunderbird until the S took over in 2003. Sonnax also warns that only a few 5R55N parts interchange with the W/S, so N owners in particular should match the old pump against this one - bolt pattern, stator support and seal ring layout - or send us year and VIN before ordering. Our 5R55 identification guide shows how to tell the three apart, and the full 5R55 parts collection lists everything else for this platform.
The transmission has to come out. With the converter off, check the converter hub where it rides in the bushing; a hub that is grooved will eat a new bushing and seal just as fast as the old one, so replace or resurface it. Install a new front seal and pump O-ring, lube the bore, run the pump bolts down evenly in a cross pattern, and set input shaft end play with the correct selective before the bell housing goes on. Flush the cooler and lines so debris from the old failure does not go straight into the new gears. Most jobs that need a pump also need the rest of the soft parts, so the 5R55W rebuild kit is the natural companion, and the filter and pan gasket kit covers the bottom of the case. Fill with Mercon V; there is no dipstick, so the level is set at the pan check plug with the engine running at operating temperature.
| Part type | Front pump assembly |
| Transmission | Ford 5R55W, 5R55S, 5R55N |
| Years | 2001 and up |
| Applications | Ford Explorer, Explorer Sport Trac, Mustang; Mercury Mountaineer; Lincoln LS |
| Shipping weight | 13.2 lb |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
It is listed for the 5R55N as well as the W and S, but the N shares only a few parts with the W/S. Compare the bolt pattern, stator support and seal ring layout against your old pump, or send us your year and VIN and we will confirm before it ships.
Often, yes. The converter hub rides in a bushing in the pump cover, and when that bushing wears the hub moves and the seal cannot hold. A complete pump assembly replaces the bushing, but also check the converter hub for wear, since a grooved hub will wear the new bushing and seal.
A new front seal and pump O-ring at minimum, plus the filter and pan gasket. If the pump failed from debris after a clutch or band failure, rebuild the rest of the transmission and flush the cooler lines, or the old metal will go straight into the new pump.
Mercon V ATF. These units have no dipstick; level is checked at a plug in the pan with the engine running and the fluid hot.
Yes. ATSG documented the 5R55N/W/S flow control valve sticking open on cold first starts, giving 40 psi or less line pressure and a delay or no engagement until it frees up. A pressure test on a cold start is the way to confirm it.
