5R55S Shift Kit 1999-2007, new and ready to install. Fits the 5R55S. Ships fast from the USA.
If your Mustang V6, Lincoln LS or Thunderbird with the 5R55S has a 1-2 slide-bump, a 2-3 flare, a soft 4-5 shift or a lockup that comes and goes when the fluid is hot, the valve body is where most of those complaints start. This is a new TransGo kit sold in the SK 5R55W box. TransGo builds one kit for the W, S and N five-speeds because they share the same basic hydraulic layout, and on an S it is the kit a technician installs during a valve body overhaul or full rebuild.
The 5R55S shifts with two bands, intermediate and overdrive, and three clutch packs, and the PCM sets apply pressure through variable force solenoids that feed modulator valves in the valve body. Sonnax points out that the TCC modulator and main regulator bores wear first on the W and S, then the VFS modulator bores, and the result is falling clutch and servo pressure that the adaptive strategy covers up until slip or ratio codes appear. The SK 5R55W targets that pressure side:
Two problems on the S look like a valve body fault and are not. The first is the solenoid pack: Sonnax ties many 5R55 solenoid failures to early Mercon V factory fill used before May 2005, and a replacement pack must be primed with fluid before install. The second is servo pin bore wear in the case, which leaks overdrive band apply oil at the servo; TransGo's sheet shows the pin wiggle test. Our 5R55S valve body symptoms guide walks through the pressure side, the 5R55S converter lockup guide covers lockup codes, and the harsh or delayed shift walkthrough sorts electrical from hydraulic faults.
The listing is titled 5R55S 1999-2007, and TransGo lists the SK 5R55W for the 5R55W, 5R55S and 5R55N from 1999 on. The S itself is a later unit. Sonnax dates the switch from the N to the S at 2003 in the Lincoln LS and Thunderbird, with the S then following the W in the Explorer and Mountaineer; the 2005-2010 Mustang V6 also uses the S. Sonnax notes the W carries a 24-tooth overdrive sun gear and the S a 38-tooth one, but the valve body side of this kit is shared. The instructions split by valve body: the S and W have no bottom plate, the N does. Match yours, or send us the year and VIN and we will confirm it. Browse the rest of the family in the 5R55 collection.
TransGo writes that the kit is for experienced professional mechanics, not a first-time valve body job. Work one valve train at a time and keep removed parts laid out in order. Inspect the center support sleeve for cracks under the bearing when the sealing rings are off, and clean the lube orifice cup plug on the stator to prevent repeat overdrive planet damage. Adjust both bands snug, back them off two turns and lock them. Refill with Mercon V and check the level with the engine running at 80 to 120 degrees F. If the valve body bores are already badly worn, a reman 5R55S valve body for 2002-2008 is a better base for the kit, and a tired solenoid pack can be replaced with the remanufactured 5R55S/W solenoid kit.
| Fits | 5R55S 1999-2007 |
| Part type | Shift Kit |
| Condition | New |
| Brand | TransGo |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
TransGo makes one kit, the SK 5R55W, for the 5R55W, 5R55S and 5R55N. The S and W share the valve body side the kit works on, so the same box covers a Mustang, Lincoln LS or Explorer with the S.
The Mustang V6 of those years uses the 5R55S, which is on TransGo's fitment list for this kit. Confirm your valve body has no bottom plate, or send us your VIN to double check.
It addresses the valve body side of a flare. If the overdrive servo pin bore is worn or the solenoid pack is failing, those need their own repair, so run the diagnosis first.
If it is an original pack on a pre-2005 unit, many technicians do. Sonnax ties solenoid failures to early Mercon V fill, and any replacement pack should be primed with fluid before installation.
The PCM adapts shift pressure as it learns the new hydraulics. Clearing adaptive values with a scan tool after the repair, then driving through all gears, helps the shifts settle sooner.
