5R55S Pump 1999, used and ready to install. Fits the 5R55S. Ships fast from the USA.
A front pump is what you replace when a 5R55-family transmission takes a long time to grab Drive or Reverse once it is hot, whines with engine speed, or slips in every gear because line pressure never comes up. This is a used 5R55 front pump assembly tagged by the rebuilder for 1999-up 5R55N, 5R55S and 5R55W units, and it has a Sonnax valve already installed. Read the fitment section before ordering: the year 1999 in the title refers to the 5R55N, not to 1999 Explorers or Rangers.
The pump is driven by the torque converter hub and supplies every psi of oil the transmission uses: line pressure for the clutches and servos, converter charge, cooler flow and lube. Inside it sits the line control valve, a plunger and canister assembly that sets how much of the pump's output is sent back to suction. Sonnax technical director Bob Warnke describes how that valve wears in these units. If the plunger sticks open, pump output is short-circuited back to the inlet and engagements are delayed until rpm comes up. If it sticks closed, line pressure climbs in Reverse, fuel economy drops and the pump body wears faster. A loose canister in its bore also cuts pump output. That is why this unit's Sonnax valve matters: the pressure-control area that wears in an original pump has been addressed.
Many of these overlap with valve body bore wear and servo bore wear, both well known on the 5R55. Our 5R55S pump failure guide walks through separating them.
Check fluid level and condition first, then put a gauge on the line pressure port. Low pressure in every range points at the pump or the main regulator. Sonnax recommends an in-car check for a stuck-open line control valve: select Reverse and unplug the solenoid connector briefly, which commands maximum pressure and can force a stuck plunger shut. If engagement suddenly improves, the pump is the problem. Keep that test short and at low rpm. For engagement problems that come from elsewhere, read our 5R55 harsh or delayed shift walkthrough.
The rebuilder's tag reads 99-up 5R55 S-W-N. According to Sonnax, the 5R55N was used from 1999 to 2002 in the Jaguar S-Type, Lincoln LS and Thunderbird, the 5R55W went into 2002-2003 Explorer and Mountaineer, and the 5R55S replaced both from 2003-2005 onward. Sonnax also warns that only a few parts interchange between the N and the W/S, so compare the bolt pattern, stator support splines and seal ring lands on your old pump with the photo, or send us your year and VIN and we will check it. A 1999 Explorer, Mountaineer or Ranger uses the older 5R55E, which this listing does not cover. Our 5R55S identification guide and the 5R55 collection will help you sort out which unit you have.
| Fits | 5R55S 1999 |
| Part type | Pump |
| Condition | Used |
| Brand | Sonnax |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. A 1999 Explorer, Mountaineer or Ranger uses the 5R55E. This pump is tagged for the 5R55N, 5R55S and 5R55W family, where 1999 refers to the 5R55N used in the Jaguar S-Type.
It replaces a worn factory pressure-control part. In these pumps the line control valve can stick open and cause delayed engagement, or stick closed and raise line pressure in Reverse, so a pump with that area already updated is a better starting point.
Sonnax notes only a few parts interchange between the N and the W/S. Compare your old pump with the photo or send your year and VIN before installing.
Mercon V. Flush out all the old fluid, because early factory fill fluid was linked to solenoid problems in these transmissions.
A front seal, pump gasket and seal rings at minimum, and inspect the torque converter hub. If the clutches are worn, do a full rebuild kit at the same time.
