5R55S Pump, remanufactured and ready to install. Fits the 5R55S. Ships fast from the USA.
A Mustang V6, Lincoln LS or 2004-2005 Explorer with a 5R55S that will not pull into gear on a cold morning, then drives normally once it warms up, is describing one of the best documented pump problems on this transmission. This is a remanufactured 5R55S front pump, bench-ready to bolt in, so you are installing a pump with fresh wear surfaces instead of rebuilding a tired one yourself. It carries a 1-year warranty.
The 5R55S pump is turned by the converter hub and supplies line pressure to the valve body, which the three variable force solenoids then trim for each clutch and band apply. Inside the pump body is a flow control valve that routes excess output back to the suction side. When that valve sticks open or its thin O-ring at the pump plate leaks, oil takes the path of least resistance back to suction and line pressure collapses. The pump cover also holds the converter hub bushing, so a worn pump can show up as a leak as easily as a shift problem.
ATSG's write-up on this exact 5R55S complaint says a gauge on either line pressure tap reads 40 psi or lower while the valve is stuck, so a cold-start pressure test separates a pump problem from a valve body or servo problem quickly. Before you get that far, check the fluid level properly - there is no dipstick, and a low level gives the same no-engage complaint. Our 5R55S pump failure symptoms guide walks through the flow control valve, regulator and bushing failures one by one, and if the car will not move at all the Mustang won't-move guide covers the other causes to rule out.
This pump is for the 5R55S. Sonnax places the S in the 2004-2005 Explorer and Mountaineer, and in the Lincoln LS and Thunderbird from 2003 when it replaced the 5R55N; the 2005-2010 Mustang V6 also uses it. Do not assume by model year alone - the 2002-2003 Explorer runs the 5R55W, and the LS ran the N before 2003. Sonnax identifies the S by its 38-tooth overdrive sun gear (the W uses 24 teeth), and the transmission code on the door label tells you which one you have. Match the old pump to this one or send us your year and VIN. Our 5R55S vs 5R55W differences guide explains the split, and everything else for this unit is in the 5R55 parts collection.
Pull the transmission and converter, inspect the converter hub for grooving before reusing it, and fit a new front seal and pump O-ring. Torque the pump bolts in a cross pattern and set input shaft end play before the bell housing goes on. If the old pump failed because clutch material or band lining went through it, the rest of the unit needs attention too; the 5R55S overhaul kit covers the seals and frictions. Flush the cooler and lines, fill with Mercon V, and set the level at the pan check plug with the engine running hot. The installation guide we cite lists roughly 11.2 quarts dry behind the 3.0 and 3.9 liter engines and 12.4 to 12.7 quarts behind the 4.0 and 4.6 liter, so have enough on hand. Afterward, clear codes and let the PCM relearn shift adapts over a few drive cycles.
| Fits | 5R55S |
| Part type | Pump |
| Condition | Remanufactured |
| Brand | OEM |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
The 2005-2010 Mustang V6 automatic uses the 5R55S, which is what this pump is built for. Confirm the transmission code on your door label, or send us your VIN, before ordering.
Those trucks use the 5R55W, not the S. The W and S look nearly identical outside, so check the door label transmission code. We list a separate 5R55W pump for the 2002-2003 trucks.
ATSG traced this complaint to the pump flow control valve sticking open in a worn sleeve, or leaking past its thin O-ring, which drops line pressure to 40 psi or lower until it frees up. A cold-start line pressure test confirms it.
Mercon V ATF. Dry fill is about 11.2 quarts behind the 3.0/3.9 liter and 12.4 to 12.7 quarts behind the 4.0/4.6 liter. There is no dipstick; set the level at the pan check plug, engine running, fluid hot.
Clear codes after the job and drive the vehicle through normal shifts for several cycles so the PCM can re-learn its shift adapts against the restored line pressure.
