This procedure covers removal and replacement of the rear differential pinion seal on a 2015-2020 Ford F-150 with 3.5L EcoBoost engine and rear-wheel drive configuration.

Warnings

Tools required

Parts

• Pinion seal × 1 — Use OEM specification
• Pinion nut (recommended) × 1 — Use OEM specification
• Rear differential gasket or RTV sealant × 1 — Motorcraft TA-357 or equivalent

Fluids

• Motorcraft 75W-140 Synthetic Gear Oil — 2 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Chock front wheels securely
3. Raise rear of vehicle and support with jack stands at frame rails
4. Allow differential to cool if vehicle was recently operated
5. Place catch pan under differential

Procedure

1. 1

   Mark driveshaft alignment
   Use paint marker or chalk to mark the relationship between the rear driveshaft and the pinion flange. This ensures proper balance during reassembly and prevents potential vibration issues.
2. 2

   Remove driveshaft
   Remove the four U-joint strap bolts at the pinion flange. Support the driveshaft and carefully lower it away from the differential. Secure the driveshaft to the frame or suspend with wire to prevent damage to the center bearing or CV joint.
   Torque spec

   Driveshaft U-Joint Straps20 Nm (15 lb-ft)
3. 3

   Drain differential fluid
   Position catch pan directly under the differential cover. Remove all differential cover bolts and carefully pry the cover away from the housing. Allow all gear oil to drain completely. Inspect drained fluid for metal particles or excessive debris which may indicate internal damage.
   ⚠Gear oil will flow out quickly once cover is removed. Ensure catch pan has adequate capacity.
   Torque spec

   Differential Cover Bolts35 Nm (26 lb-ft)
4. 4

   Mark pinion rotating torque
   Using an inch-pound torque wrench with a socket on the pinion nut, rotate the pinion flange through several revolutions and record the rotational torque required. This measurement is critical for maintaining proper pinion bearing preload. Typical values range from 16-29 inch-pounds for used bearings.
5. 5

   Mark and remove pinion nut
   Mark the position of the pinion nut relative to the pinion shaft threads using paint marker. This provides a reference for reinstallation depth. Hold the pinion flange with a holding tool or large channel locks, then remove the pinion nut. Keep the nut if it will be reused, though a new nut is recommended.
6. 6

   Remove pinion flange
   The pinion flange should pull off by hand once the nut is removed. If stuck, use a puller or carefully tap the flange with a dead blow hammer while supporting it to prevent dropping. Note the orientation and any alignment marks.
7. 7

   Remove old pinion seal
   Use a seal puller or carefully pry out the old pinion seal from the differential housing. Take care not to damage the seal bore surface in the housing. Clean the seal bore thoroughly with brake cleaner and inspect for any scoring or damage that could cause the new seal to leak.
8. 8

   Install new pinion seal
   Lightly coat the outer edge of the new seal with gear oil. Position the seal squarely in the bore with the seal lip facing inward toward the differential. Using a seal driver or appropriately sized socket, carefully tap the seal into place until it is flush with the housing face. Ensure the seal is not cocked or damaged during installation.
9. 9

   Reinstall pinion flange
   Lightly coat the pinion seal contact surface on the flange with clean gear oil. Slide the pinion flange onto the pinion shaft in the original orientation. Ensure the flange seats fully onto the shaft.
10. 10

    Install and torque pinion nut
    Thread the pinion nut (new or original) onto the pinion shaft. Hold the flange and tighten the nut gradually. Tighten to the marked position noted during disassembly, then check rotating torque with an inch-pound torque wrench. Continue tightening in small increments until the rotational torque matches the value recorded in step 4. Do not exceed 3 additional inch-pounds above the original value.
    ⚠️Over-tightening the pinion nut will collapse the pinion bearing spacer and ruin the bearing preload. If proper preload cannot be achieved, stop and consult a professional or disassemble for bearing replacement.
11. 11

    Clean and prepare differential cover
    Remove all old gasket material from both the differential housing and cover using a scraper and wire brush. Clean both surfaces thoroughly with brake cleaner. If using a gasket, ensure surfaces are completely dry. If using RTV sealant, apply a continuous 1/8 inch bead to the cover sealing surface.
12. 12

    Reinstall differential cover
    Position the cover with gasket or RTV onto the differential housing. Install all cover bolts hand-tight, then torque in a crisscross pattern to ensure even sealing and prevent warping.
    Torque spec

    Differential Cover Bolts35 Nm (26 lb-ft)
13. 13

    Refill differential
    Remove the differential fill plug on the front of the housing. Using a fluid pump or funnel with hose, add Motorcraft 75W-140 Synthetic Gear Oil until fluid reaches the bottom of the fill hole. Install and tighten the fill plug. Total capacity is approximately 2 quarts.
14. 14

    Reinstall driveshaft
    Align the marks made during disassembly and position the driveshaft onto the pinion flange. Install the four U-joint strap bolts and tighten evenly in a crisscross pattern to prevent binding.
    Torque spec

    Driveshaft U-Joint Straps20 Nm (15 lb-ft)

Reassembly

1. Allow RTV sealant to cure for 1 hour before driving if used instead of gasket
2. Lower vehicle from jack stands carefully
3. Remove wheel chocks

Verification

• Start engine and verify no leaks from pinion seal area
• Test drive vehicle and verify no abnormal differential noise or vibration
• Recheck differential fluid level after test drive and top off if necessary
• Inspect pinion seal area for leaks after 50-100 miles of operation

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