4R70W Sun Shell

When a 4R70W loses second gear and overdrive at the same time, or Reverse disappears while Drive still pulls, the sun shell is high on the list of suspects. This is a used OEM 4R70W sun shell with the reverse sun gear, the part shown in the photo, for Ford F-150 and Expedition trucks, Crown Victoria and Grand Marquis police and fleet cars, Town Cars, Mustangs and Explorers that use this four-speed. It is the right repair when teardown shows a cracked stamping, rounded drive tabs or a damaged sun gear.

What the sun shell does in a 4R70W

The 4R70W builds all four forward speeds and Reverse from one Ravigneaux gearset with two sun gears. The sun shell is the steel bell that ties the reverse drum to the large reverse sun gear in the middle of that gearset. Hold it, through the intermediate clutch and diode for second or the overdrive band for fourth, and the gearset gives 1.55:1 and 0.70:1. Drive it through the reverse clutch and you get Reverse at 2.32:1. Because the same stamping carries reaction torque in second, fourth and Reverse, a crack at the base of the gear takes several ranges out at once.

ATRA's interchange notes show Ford attacked exactly that weak spot. From 2004 the shell was made stronger, as a two-piece riveted part and later a one-piece part, with thicker metal at the chamfer where the gear meets the shell.

Symptoms of a cracked or stripped 4R70W sun shell

• No second and no overdrive, with first and third still working
• No Reverse, or Reverse that bangs and then slips
• A 1-2 or 3-4 flare with clean fluid and no burnt clutch smell
• Ratio error codes such as P0732 or P0734 with no solenoid fault
• Steel chunks on the pan magnet, sometimes with pieces of the stamping

How to confirm it before you order

A worn intermediate clutch, a slipping overdrive band or a bad solenoid can also take out second and fourth, so scan for codes and check line pressure first. The F-150 shift problems guide walks through separating electrical and pressure faults from hard-part failures, and the Expedition common problems guide covers the same checks on the bigger trucks. If the codes and pressure are clean and the magnet holds steel instead of friction material, plan on a teardown. A failed shell is easy to see once the gear train is out: look for a hairline crack around the gear base and inspect the drive tabs and sun gear teeth.

Fitment

This shell is listed for the 4R70W without a year range. The 4R70W ran from 1993 through 2004 depending on the vehicle and was followed by the 4R75W and the electronic 4R70E/4R75E, and the sun shell changed along the way. ATRA reports that the 2004-up shell has a lower height between the sun gear and the bearing surface, and that the late shell, its bearing and the forward sun gear must be changed together or end play will be wrong. ATRA also notes the 4R70E/4R75E shell is non-magnetic so the input speed sensor can read through it, and a magnetic shell in those units causes harsh or no shifting and speed sensor codes. Match your original's height, tab count and gear before ordering, or send us your year and VIN. Year-specific versions include the 1993 4R70W sun shell and the 2004 4R70W sun shell, and everything else for this family is in the 4R70W collection.

Install notes

• Replace the thrust bearing under the sun gear and confirm it seats flat.
• Check the forward sun gear and the reverse drum lugs; a broken shell often damages both.
• Inspect the planetary carrier pinions and thrust washers for debris damage.
• Measure end play when the unit is together and correct it with the selective washer.
• Clean the case, cooler and lines of all metal, and replace the filter.
• Refill with MERCON V, the fluid Ford specifies for the 4R70W.

Does this sun shell fit a 2004 or later 4R70W or 4R75W?

Not without matching parts. Ford changed the shell in 2004, and ATRA says the late shell, bearing and forward sun gear must be swapped as a set or end play will be off. Send us your year and VIN and we will confirm.

Can I use it in a 4R70E or 4R75E?

Those units need a non-magnetic sun shell so the input speed sensor can read the forward drum. A standard 4R70W shell can cause harsh or no shifts and speed sensor codes there.

What symptoms point to a broken sun shell?

No second and no overdrive with first and third still working, or no Reverse. Clean fluid with steel pieces on the magnet points to the shell rather than burnt clutches.

What should I replace along with the sun shell?

The thrust bearing under the sun gear, plus anything damaged by debris, usually the forward sun gear, the reverse drum or the planetary. Change the filter and flush the cooler.

What fluid does the 4R70W use?

MERCON V. Do not substitute a MERCON LV or ULV fluid unless Ford specifies it for your vehicle.

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