5R55W Sun Shell

The 5R55W went into the 2002 and 2003 Ford Explorer and Mercury Mountaineer, and many of those trucks are now on their second or third transmission job. If yours came apart with a split sun shell, worn teeth where the shell meets its gear, or a pitted bearing race inside the shell, this listing is a new original Ford replacement. It is the shell only, listed as a 55-tooth design that runs on an internal bearing, and it is shared across the 5R55W, 5R55S and 5R55N.

What the sun shell does in a 5R55W

The W is a clutch-and-band five-speed. It dropped the intermediate clutch and sprag of the 5R55N, so shift timing depends on the PCM releasing one band or clutch exactly as the next applies. The sun shell sits between the direct clutch drum and the sun gear of the main gear set and carries direct-clutch torque into that gear. The direct clutch is the apply element for reverse and works with the overdrive band for fifth, and when the intermediate band holds the direct drum, the shell holds the sun gear. That shared duty is why a damaged shell rarely takes out just one gear.

Symptoms that point toward the sun shell

• Reverse that engages late, slips or disappears while the forward gears still work
• A bind or flare on band-to-clutch shifts after the unit has already been checked for servo bore wear
• Noise that rises with road speed, which on the W can also come from the front planet bearing
• Steel particles on the pan magnet and filter
• Ratio codes such as P0730 that return after the valve body has been serviced

Rule out the common W failures first

The W has a few well-known weak spots that look like hard-part failure. Sonnax documents a front planet bearing on the W that was especially prone to failure, with the bearing cage on the sun-gear side stamped out, and the servo pin bores wear and bleed off band apply pressure. Our 5R55W noise diagnosis guide separates bearing whine from gear noise, and the 5R55 harsh or delayed shift walkthrough covers the hydraulic causes. Order the shell when you can see the damage on it.

Fitment

Sonnax places the W in the 2002-2003 Explorer and Mountaineer before the 5R55S took over for 2004-2005. This shell is listed for the W, the S and the N, but Sonnax cautions that most N hard parts do not carry over to the W and S, so treat N fitment as something to confirm by comparison. The W used a 24-tooth overdrive sun gear where the S used 38 teeth, but that is the front overdrive set, not this shell. Compare the tooth count and internal bearing to your old part, or send us your year and VIN. Browse the whole family on the 5R55 transmission page, or see the earlier 5R55W sun shell listing if yours is a different version.

Install notes

• Install the internal bearing and thrust washers in the factory order and measure end play before final assembly
• While the gear train is out, inspect the front planet bearing and sun gear; Sonnax notes the original bearing could not be replaced without disassembling the planet
• Use Mercon V and check the level hot through the fluid level plug, as Ford's procedure describes
• Clear adaptive tables and road test so the PCM relearns shift pressures

Most shells get replaced during an overhaul, so pair it with a 5R55W overhaul kit and inspect the 5R55W planetary while you are in there.

Does this fit a 2002 or 2003 Ford Explorer with the 5R55W?

Yes, it is listed for the 5R55W used in those trucks. Compare the 55-tooth engagement and internal bearing to the shell you removed, or send us the VIN and we will confirm.

Does it include the sun gear or the bearing?

The listing is for the shell only. Inspect your sun gear and bearing and replace them if they show wear.

Can I use this shell in a 5R55S?

It is listed for the 5R55S as well. The common W-to-S difference is the overdrive sun gear tooth count, which is a separate part in the front gear set.

My 5R55W whines. Is it the sun shell?

Possibly, but the W's front planet bearing is a better-known source of whine. Inspect that bearing and the sun gear side of the planet when the unit is apart.

What fluid does the 5R55W take?

Ford specifies Mercon V. Check the level hot through the fluid level plug after the job and run a relearn.

• 5R55 Harsh or Delayed Shifts: A Diagnostic Walkthrough
• 5R55W Noise Diagnosis (Whine vs. Clunk)
• 5R55W P0730: Incorrect Gear Ratio Causes and Fix
• 5R55W Explorer Common Problems and Fixes