This procedure drains and refills the rear differential with fresh synthetic gear oil to maintain proper lubrication and extend component life.

Warnings

Tools required

Parts

• Differential cover gasket × 1 — Use OEM specification
• RTV silicone gasket maker (if gasket not used) × 1 — Motorcraft TA-31 or equivalent

Fluids

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

Preparation

1. Park vehicle on level surface and engage parking brake
2. If recently driven, allow differential to cool for at least 30 minutes
3. Raise rear of vehicle and support securely on jack stands at frame rails
4. Ensure adequate clearance to work under rear axle housing
5. Locate the differential cover at rear of axle housing (oval-shaped cover with 10 bolts)

Procedure

1. 1

   Clean differential cover area
   Use a wire brush and brake cleaner to remove dirt, road grime, and debris from around the differential cover and bolt heads. This prevents contamination when opening the cover.
2. 2

   Loosen differential cover bolts
   Using a 10mm socket, loosen all differential cover bolts approximately 2-3 turns each. Start with the upper bolts first. Do not fully remove any bolts yet.
3. 3

   Position drain pan and remove lower bolts
   Place drain pan directly under the differential cover. Remove the bottom bolts first, leaving 2-3 upper bolts loosely in place. Allow fluid to drain from the bottom edge of the cover. The differential holds approximately 2 quarts of fluid.
   ⚠Fluid will drain quickly once lower bolts are removed. Position drain pan carefully to avoid spills.
4. 4

   Remove cover completely
   Once most fluid has drained, remove the remaining upper bolts and carefully pry the cover away from the housing. Be prepared for additional fluid to drain. Allow cover to drain completely into pan.
5. 5

   Inspect internal components
   With cover removed, visually inspect the ring gear, pinion gear, and inside of housing for metal shavings, scoring, or damage. A small amount of fine metallic paste on the magnetic drain plug is normal. Excessive metal particles or chunks indicate abnormal wear requiring further diagnosis.
   ℹ️If metal chunks or heavy debris are found, the differential may require professional inspection before continuing.
6. 6

   Clean cover and housing mating surfaces
   Use a razor scraper to completely remove all old gasket material and RTV from both the differential cover and housing mating surface. Clean surfaces thoroughly with brake cleaner and wipe dry. Both surfaces must be completely clean and free of oil residue for proper sealing.
7. 7

   Prepare new gasket or RTV
   If using a pre-cut gasket, ensure it aligns properly with all bolt holes. If using RTV silicone, apply a continuous 3mm bead around the inside of the bolt holes on the cover, ensuring the bead surrounds all bolt holes. Allow RTV to set for 5 minutes before installation if specified by manufacturer.
8. 8

   Install differential cover
   Carefully position the cover with gasket onto the housing, aligning all bolt holes. Insert all bolts hand-tight first to ensure proper alignment. Do not cross-thread bolts.
9. 9

   Torque cover bolts to specification
   Using a torque wrench, tighten the differential cover bolts in a crisscross pattern starting from the center and working outward. Torque all bolts to specification in multiple passes: first to 15 Nm, then to final specification.
   Torque spec

   Differential Cover Bolts35 Nm (26 lb-ft)
10. 10

    Refill differential with gear oil
    Locate the fill plug on the front of the differential housing (10mm bolt). Remove fill plug. Using a fluid pump or fill bottle with hose, add Motorcraft 75W-140 synthetic gear oil through the fill hole until oil begins to drip from the fill hole. This indicates proper fill level (approximately 2 quarts total). Reinstall fill plug hand-tight, then torque if specification available.
    ℹ️Fill until fluid reaches the bottom of the fill hole. Overfilling can cause seal leakage and overheating.
11. 11

    Check for leaks
    Wipe down the entire differential cover and fill plug area. Wait 5 minutes and inspect all sealing surfaces for any signs of fluid leakage. Address any leaks before lowering vehicle.

Reassembly

1. If RTV was used, allow 1 hour cure time before driving to ensure proper seal
2. Lower vehicle from jack stands carefully
3. Dispose of used gear oil at an approved recycling facility

Verification

• Start engine and allow to idle for 1 minute
• With vehicle still on level ground, recheck fill plug area and differential cover for any signs of leakage
• Test drive vehicle for 5-10 minutes, then recheck for leaks while differential is warm
• Monitor for unusual noises from rear axle during test drive, which should operate smoothly and quietly

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