Differential Cover Gasket

Replace the rear differential cover gasket to repair leaks, including draining the old gear oil, cleaning mating surfaces, installing a new gasket, and refilling with fresh lubricant.

Warnings

Tools required

Parts

• Rear differential cover gasket × 1 — Use OEM specification or high-quality aftermarket
• RTV silicone gasket maker (optional sealant) × 1 — Ultra Grey or equivalent

Fluids

• 80W-90 GL-5 rear differential fluid — 3.5 qt

Preparation

1. Park vehicle on level ground and engage parking brake firmly.
2. Place wheel chocks in front of both front wheels.
3. Raise the rear of the vehicle using a floor jack at the rear axle housing or frame, then support securely on jack stands placed under the frame rails.
4. Allow differential to cool if vehicle was recently driven.
5. Position drain pan under the rear differential cover to catch approximately 3.5 quarts of gear oil.

Procedure

1. 1

   Loosen differential cover bolts
   Locate the differential cover bolts (commonly 10, but count yours to confirm) securing the rear differential cover to the axle housing. Using a 1/2" or 9/16" socket (verify size before proceeding), loosen all bolts approximately 3-4 turns each, but do not remove them completely yet. Start with the bolts at the top of the cover and work your way around. Verified detail (1972 Ford F-100 rear differential covers typically have 12 bolts, not 10. This count appears throughout the procedure and needs verification for the specific axle type (likely Ford 9-inch).): Locate the bolts securing the rear differential cover to the axle housing (typically 12 bolts on Ford 9-inch axles). Using a 1/2" or 9/16" socket (verify size before proceeding), loosen all bolts approximately 3-4 turns each, but do not remove them completely yet.
2. 2

   Break cover seal and drain fluid
   Carefully remove the bottom two bolts completely while holding the cover in place. Gently pry the bottom edge of the cover away from the housing using a flathead screwdriver or gasket scraper to break the seal. Allow the gear oil to drain into the pan. Once flow slows, remove the remaining bolts and carefully pull the cover away from the housing. Tilt the cover to drain any remaining oil. Be prepared for additional oil to drain from the housing opening.
3. 3

   Remove old gasket material from cover
   Place the differential cover on your work surface with the inner surface facing up. Using a gasket scraper or plastic razor blade, carefully remove all old gasket material and RTV sealant from the cover's mating surface. Follow up with a wire brush to remove stubborn residue. Clean the surface thoroughly with brake cleaner and wipe dry with a clean shop rag. The mating surface must be completely clean and free of debris for proper sealing.
4. 4

   Clean housing mating surface
   Using the same technique, carefully scrape and brush all old gasket material from the differential housing mating surface. Be careful not to allow debris to fall into the differential housing. Stuff a clean rag loosely into the opening to catch any falling particles. Once scraped, remove the rag and wipe the surface clean with brake cleaner. Inspect both the cover and housing surfaces to ensure they are flat and free of gouges or warping.
5. 5

   Inspect differential internals
   With the cover removed, visually inspect the ring gear teeth for excessive wear, chipping, or damage. Check for metal shavings or debris in the bottom of the housing (small amounts of fine metallic paste on the magnet are normal). If heavy debris or damaged gears are present, further diagnosis is required before reassembly.
6. 6

   Install new gasket on cover
   Position the new differential cover gasket on the cover, aligning all bolt holes. If using RTV sealant as supplemental insurance, apply a thin continuous bead (approximately 1/8" diameter) around the cover on the gasket side, staying inboard of the bolt holes. Some mechanics prefer RTV alone without a gasket; if using this method, apply a 1/8" bead directly to the clean cover flange.
7. 7

   Reinstall differential cover
   Carefully position the differential cover with gasket against the housing, ensuring the gasket stays in place and all bolt holes align. Start all bolts by hand to ensure proper threading. Once all bolts are started, tighten them in a crisscross pattern (alternating top to bottom, side to side) to draw the cover evenly against the housing. Make multiple passes, gradually tightening each bolt until all are snug. Final torque specification: 15-20 ft-lbs in a crisscross pattern (verify against factory service manual for your specific axle).
8. 8

   Refill differential with gear oil
   Locate the differential fill plug on the front or side of the differential housing (9/16" or 3/8" square drive plug). Remove the fill plug using the appropriate tool. Using a fluid pump or funnel with a long flexible hose inserted into the fill hole, add 80W-90 GL-5 gear oil. Fill until oil begins to seep from the fill hole, indicating proper level (approximately 3.5 pints). Reinstall the fill plug and tighten firmly.
9. 9

   Clean up and lower vehicle
   Wipe down the differential cover and surrounding area to remove any spilled gear oil. Check underneath the cover for any signs of leakage. Remove the drain pan and properly store or dispose of the used gear oil. Carefully lower the vehicle from the jack stands and remove the wheel chocks.

Reassembly

1. If RTV sealant was used, allow 1-2 hours curing time before driving to prevent leaks.
2. Double-check that the differential fill plug is installed securely.
3. Dispose of used gear oil at a recycling facility or auto parts store that accepts used fluids.

Verification

• Start the vehicle and allow it to idle briefly, then shut off and inspect the differential cover for any signs of leakage.
• After the first short drive (5-10 miles), recheck the differential cover for leaks, especially around the bottom edge and bolt heads.
• Verify the differential fill plug is secure and not leaking.
• After 50-100 miles, perform a final inspection to ensure the gasket has properly seated and no leaks have developed.

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