5R55W Overhaul Gasket and Seal Kit, Explorer 2002-2010

If your Explorer, Mountaineer, Sport Trac or 2005-2010 Mustang leaves a red puddle under the bellhousing or the pan rail, or the transmission is already on the bench and you need every gasket and seal in one box, this is the kit. It is a complete reseal set for the Ford 5R55W and 5R55S: a cork pan gasket, the pump and case gaskets, piston and drum lip seals, the front pump seal, the rear extension seal and the small O-rings for the solenoid pack and case connector. It crosses to the common kit numbers KP53900SX, K56900KX, T16002G and T16002GA, so it can be matched against a rebuilder's parts list. Frictions, steels and a filter are not in the box.

What a gasket and seal kit does in a 5R55W or 5R55S

This five-speed is run almost entirely by solenoids. Transmission Digest counts four on/off shift solenoids, a PWM converter clutch solenoid and three variable force solenoids that set apply pressure for individual clutches and servos. Every one of those circuits ends at a rubber seal: a piston lip seal in a drum, a servo cover O-ring, or the O-rings where the solenoid body meets the valve body. When those seals harden, oil the solenoids meant for a clutch leaks back to the pan, and the computer can only respond by commanding more pressure. The external gaskets and the front and rear seals are the other half of the job. They are what keep the fluid level right on a unit that has no dipstick, so a slow leak is easy to miss until the transmission is low and slipping.

Symptoms this kit addresses

• A drip at the bellhousing seam, usually the front pump seal or the pump body O-ring
• Seepage around the pan rail or a wet rear extension housing at the driveshaft yoke
• A lazy engagement into drive or reverse after the vehicle sits overnight
• A flare on the 2-3 shift or into overdrive as servo cover O-rings bleed apply oil
• A clutch pack that slips under load while the frictions still measure in spec

How to confirm the leak or pressure loss first

Clean the case, drive the truck, and find the wet spot before buying anything. Our 5R55W fluid leak guide walks through the usual locations, and Mustang and Lincoln owners can use the 5R55S leak guide. If the complaint is shift quality rather than a leak, do not assume seals. Sonnax reports that the overdrive and intermediate servo pin bores in the case wear and leak apply oil, and that the VFS modulator bores in the valve body wear until the solenoids cannot supply full pressure. New rubber fixes neither. The 5R55 harsh or delayed shifts walkthrough lays out the checks in order.

Fitment

This kit is listed for the 5R55W and 5R55S in the 2002-2010 Ford Explorer with the 4.0L V6 or 4.6L V8, 2007-2010 Explorer Sport Trac, 2002-2010 Mercury Mountaineer, 2005-2010 Mustang with the 4.0L or 4.6L, 2003-2006 Lincoln Aviator, 2003-2006 Lincoln LS and 2003-2005 Thunderbird. The W and S share the case and nearly all of the soft parts. Sonnax separates the W, with a 24-tooth overdrive sun gear, from the S, with a 38-tooth gear, but that change is in the hard parts. The kit does not fit the earlier 5R55N used in the Lincoln LS and Thunderbird before 2003, or the 5R55E in the Ranger and 1997-2001 Explorer. Check the transmission code on the door-jamb label or send us your year and VIN to confirm. Every part we carry for this family is on the 5R55 transmission parts page.

Install notes

• Replace every lip seal and O-ring as each drum and servo comes apart, not just the ones that look bad. The cost is in the labor, not the rubber.
• Lubricate new seals with assembly gel or clean ATF before the pistons go back into their drums, and air-check each circuit before the case is closed.
• Set the cork pan gasket dry and tighten the pan bolts in a criss-cross pattern so the cork does not squeeze out at one corner.
• A filter is not included. Add the 5R55W/5R55S filter and pan gasket kit so the unit goes back together with a clean filter.
• The solenoid body uses eight bolts to the valve body; Ford service information gives 71 lb-in in sequence and warns that overtorquing damages it. If the pack is tired, the 5R55W solenoid kit is the time-saving add-on.
• Refill with Mercon V and set the level at the T30 Torx check plug with the engine running at operating temperature.

What is in this kit and what is not?

It includes the cork pan gasket, pump and case gaskets, piston and drum lip seals, the front pump seal, the rear extension seal and the O-rings for the solenoid pack and case connector. It does not include frictions, steels, bands or a filter.

Does it fit my 2006 Mustang?

The kit is listed for 2005-2010 Mustangs with the 4.0L or 4.6L and the 5R55S automatic. Confirm the transmission code on the door-jamb label, or send us your VIN and we will check it.

Can I replace just the front pump seal without pulling the transmission?

No. The front pump seal sits behind the torque converter, so the transmission has to come out. Because the labor is the same, most owners reseal the whole unit with this kit while it is out.

Will a reseal fix slipping or a flare into overdrive?

It will if the cause is hardened servo or piston seals. If the servo pin bores in the case or the valve body bores are worn, new seals will not hold pressure, so air-check the circuits and inspect the bores during the teardown.

What fluid does it take and how do I check the level?

Mercon V. There is no dipstick. The level is set at the T30 Torx check plug with the engine running and the fluid at operating temperature.

• 5R55W Fluid Leak Common Spots
• 5R55S Fluid Leak Common Spots
• 5R55 Harsh or Delayed Shifts: A Diagnostic Walkthrough
• 5R55S Identification Guide: 5R55S vs W, N and E