5R55S Shift Kit 1999

A 5R55S that stops locking the converter once the fluid is hot, shudders at a steady 45 to 60 mph, or sets P1740 is one of the most common complaints on the 2005-2010 Mustang V6, the 2003-2006 Lincoln LS and the 2003-2005 Thunderbird. Most owners assume the torque converter is finished. This new TransGo SK 5R55W shift kit is built around a different conclusion: TransGo's own instructions state that lockup problems on this unit are usually valve body caused, not converter caused. The same kit also covers the 2-3 flare, slide-bump shifts and pump-related no-move faults that show up on high-mileage S units.

What the shift kit does in a 5R55S

TransGo makes one kit for the S, W and N, but the S and W share a valve body with no bottom plate, and the instruction sheet gives them their own page. On an S valve body the kit does four jobs:

• Lockup circuit. The original spring, lockup valve, bushing and inner valve come out. A new lockup valve, white spring, bushing and inner valve go in, adding lockup capacity while keeping a smooth apply. TransGo notes it works with all model converters, so a stock or aftermarket converter both benefit.
• EPC reliefs. Two original end plugs and retainers are replaced with EPC relief assemblies, which cap line pressure spikes.
• Springs. New yellow springs replace originals, and a new green spring replaces the RS/ISA select spring next to the OD servo control valve.
• Pump side. An upgraded pump flow control assembly, a pump alignment tool and high-temperature direct clutch sealing rings for the center support.

Symptoms on a 5R55S that match this kit

• No converter lockup when hot even though the fluid and filter look clean
• Lockup shudder or slip at cruise, with P1740 stored
• Gear ratio codes P0732, P0733 or P0735
• 1-2 slide-bump, 2-3 flare or 4-5 slide-bump
• Won't move after warm-up, or a whine from the front pump

How to confirm the cause before buying

Start with the lockup complaint, because it is the one most often misdiagnosed. Our 5R55S lockup explainer shows how the PCM commands the converter clutch, and the 5R55S converter shudder guide separates fluid, valve body and converter causes. TransGo's rule of thumb is that hot no-lockup with good-looking fluid points to the valve body. If the complaint is a burned overdrive band or a 2-3 flare instead, check the OD servo pin before anything else: TransGo's sheet says to wiggle the pin, and a loose pin means a worn case bore that no shift kit can seal. The 5R55S valve body symptoms guide covers the remaining pressure faults.

Fitment

This listing is titled 5R55S 1999 because TransGo catalogs the SK 5R55W from 1999 on; the printed instruction sheet reads S/W/N 1999-10. No vehicle actually used an S in 1999. The S replaced the N in the Lincoln LS and Thunderbird for 2003, appears in the 2005-2010 Mustang V6, and was also used in later Explorer and Mountaineer models alongside the W. The kit carries interchange number T54165B. Confirm you have the S/W valve body with no bottom plate when the pan is off, and if you are unsure which 5R55 you have, send us your year and VIN. Every part for this family is in our 5R55 transmission collection.

Install notes

TransGo states this is not a do-it-yourself kit; it is for experienced transmission technicians. Keep each valve train in order as it comes out, and after fitting the new lockup valve make sure it strokes freely to the bottom of its bore before final assembly. The lockup bushing retainer leaves a small burr in the groove, which has to be scraped off before the bushing is gently pried out. On reassembly, align the pump halves on the stator spline before the front seal goes in and torque the pump bolts to 18 ft-lb. Fill with Mercon V. The S has its fill plug on the side of the case; the level is correct only when fluid runs in a steady stream from the Allen plug in the center of the pan drain plug with the engine running in Park and the fluid at 80 to 120 degrees F. An S that has already burned clutches needs the 5R55S banner rebuild kit along with this kit, and a pack with intermittent shift codes is best replaced with our 5R55W/5R55S solenoid block pack.

Will this kit fit my 2007 Mustang V6 with the 5R55S?

Yes. TransGo's SK 5R55W covers the 5R55S, 5R55W and 5R55N, and the 2005-2010 Mustang V6 uses the S with the no-bottom-plate valve body this kit's S/W page is written for.

The listing says 1999. Is there a 1999 5R55S?

No. The 1999 date is the start of TransGo's catalog coverage for the kit. The 5R55S itself first appeared in 2003 Lincoln LS and Thunderbird models. Send us your year and VIN if you want us to confirm your unit.

My S has no lockup when hot and P1740. Do I need a converter?

Not necessarily. TransGo states lockup problems on this unit are usually valve body caused, and the kit replaces the lockup valve, bushing, inner valve and spring. If the fluid and filter look clean, the valve body is the first place to look.

Can this kit be installed without removing the transmission?

Only the valve body portion. The pump flow control assembly, pump alignment and direct clutch rings require the pump and center support to come out, so the full kit is normally installed during a rebuild.

What fluid does the 5R55S take after installing the kit?

Mercon V. Check the level with the vehicle level, engine running in Park and the fluid between 80 and 120 degrees F, filling until a steady stream runs from the check hole in the drain plug.

• 5R55S Torque Converter Lockup Explained
• 5R55S Torque Converter Shudder
• 5R55S Valve Body Symptoms
• 5R55S Mustang Shift Problems
• 5R55 Harsh or Delayed Shifts: A Diagnostic Walkthrough