Axle Seal - Rear

Replace the rear axle seal on a 1972 Ford F-100 with 302ci V8, including differential fluid drain and refill.

Warnings

Tools required

Parts

• Rear axle seal (driver or passenger side) × 1 — Use OEM specification for Ford 9-inch rear axle
• Differential cover gasket × 1 — Use OEM specification or RTV silicone gasket maker
• Axle flange bolts (if damaged) × 4 — Use OEM specification

Fluids

• 80W-90 GL-5 gear oil — 3.5 qt

Preparation

1. Park vehicle on level ground and place wheel chocks in front of front wheels.
2. Loosen the rear wheel lug nuts on the side requiring seal replacement while vehicle is still on the ground.
3. Raise rear of vehicle with floor jack and support securely on jack stands placed under the frame rails.
4. Remove the rear wheel on the side requiring seal replacement.
5. Place drain pan under differential cover.

Procedure

1. 1

   Drain differential fluid
   Drain the differential fluid by removing the drain plug (if equipped) or by removing the fill plug and siphoning. Note: the Ford 9-inch axle uses a removable front third-member carrier and has no rear inspection cover, so cover removal is not part of this procedure.
2. 2

   Remove axle shaft retainer bolts
   Locate the 4 nuts/bolts securing the axle shaft bearing retainer plate to the flange at the outer end of the axle housing. Access them through the holes in the axle flange, rotating the shaft to align each. Remove all 4 fasteners and keep the retainer plate with them for reassembly. Verified detail (On the Ford 9-inch rear axle, the retainer plate bolts are accessed from the rear of the axle flange, not through an inspection hole in the differential cover. The bolts secure the retainer to the axle housing from the outside.): Locate the 4 nuts securing the axle shaft retainer plate to the backing plate studs, accessible from the brake drum side. Remove all 4 retainer nuts using a 9/16" socket and ratchet. Keep the retainer plate with the nuts for reassembly.
3. 3

   Remove axle shaft
   Carefully pull the axle shaft straight out of the axle housing. Carefully pull the axle shaft straight out of the axle housing. The Ford 9-inch axle uses a bolt-in retainer plate (removed in the previous step) rather than a C-clip, so once the retainer bolts are out the shaft is free to slide out. A slide hammer may be needed if the axle bearing is a press fit. Be prepared for residual gear oil to drain from the axle tube. Set the axle shaft on a clean surface. Verified detail (The 1972 Ford F-100 with 9-inch rear axle does not use C-clips to retain axle shafts. The 9-inch uses a retainer plate and bearing that holds the shaft in place. C-clips are used in Ford 8.8-inch and some 8-inch rear axles, not the 9-inch.): Carefully pull the axle shaft straight out of the axle housing. The shaft should slide out once the retainer plate bolts are removed. Be prepared for residual gear oil to drain from the axle tube. Set the axle shaft on a clean surface.
4. 4

   Remove old axle seal
   Using a seal puller or slide hammer with seal puller attachment, carefully extract the old axle seal from the axle tube. Hook the puller behind the inner lip of the seal and pull straight out. Avoid damaging the seal bore surface in the axle housing. If the seal is stubborn, work around the perimeter to break it free evenly.
5. 5

   Clean seal bore
   Thoroughly clean the axle seal bore in the housing using shop rags and solvent if necessary. Remove all old seal material, rust, and debris. Inspect the seal bore surface for scoring or damage that could cause the new seal to leak. The surface should be smooth and clean.
6. 6

   Inspect axle shaft and bearing
   Inspect the axle shaft seal surface where the seal lip rides. Look for grooves, pitting, or scoring that could cause premature seal failure. Minor imperfections can be smoothed with fine emery cloth. If damage is severe, the axle shaft must be replaced. Check the axle bearing for roughness or play; replace if necessary.
7. 7

   Install new axle seal
   Lightly coat the outer diameter of the new seal with gear oil. Position the seal squarely in the axle tube bore with the lip facing inward toward the differential. Using an axle seal driver or large socket that matches the seal outer diameter, carefully tap the seal into place until it is fully seated and flush with the axle housing face. Drive evenly around the perimeter to avoid cocking the seal.
8. 8

   Lubricate and install axle shaft
   Coat the axle shaft seal surface and splines with clean gear oil. Carefully slide the axle shaft into the housing, aligning the splines with the differential side gear. Push the shaft in completely until the splines fully seat in the side gear and the bearing retainer plate contacts the housing flange. Verified detail (The 9-inch rear axle does not use C-clips. The axle shaft is retained by the retainer plate and bearing, not by a C-clip engaging a groove in the differential.): Coat the axle shaft seal surface and splines with clean gear oil. Carefully slide the axle shaft into the housing, aligning the splines with the differential side gear. Push the shaft in completely until it is fully seated against the differential.
9. 9

   Install axle retainer
   Position the axle retainer plate over the axle flange and align with the bolt holes. Install all 4 retainer bolts and tighten in a cross pattern to ensure even pressure. Tighten securely but avoid overtightening, which can distort the retainer plate.
10. 10

    Install differential cover
    Install a new gasket on the differential cover or apply a 1/8" bead of RTV silicone to the cover flange. Position the cover on the differential housing and install all cover bolts. Tighten in a cross pattern starting from the center and working outward to ensure even gasket compression and prevent leaks.
11. 11

    Refill differential with gear oil
    Locate the differential fill plug on the housing. Note that the Ford 9-inch uses a front-loading removable third-member carrier, so it typically has no rear inspection cover; the fill plug is on the housing itself. Remove the fill plug. Using a fluid pump or squeeze bottle, add 80W-90 GL-5 gear oil through the fill hole until oil begins to seep from the fill hole opening. If the axle is equipped with a Traction-Lok limited-slip differential, add the required friction modifier additive. The correct level is at the bottom of the fill hole. Install and tighten the fill plug.
12. 12

    Reinstall wheel and lower vehicle
    Reinstall the rear wheel and hand-tighten all lug nuts in a star pattern. Lower the vehicle until the tire just touches the ground. Torque the lug nuts to specification in a star pattern. Fully lower the vehicle and remove jack stands.

Reassembly

1. If replacing both axle seals, repeat the entire procedure for the opposite side.
2. Wipe down the differential housing and surrounding area to remove any spilled gear oil.
3. Dispose of used gear oil properly at a recycling center or auto parts store.

Verification

• Check for gear oil leaks around the differential cover and axle seal area immediately after completion.
• Drive the vehicle 10-15 miles and re-inspect the axle seal and differential cover for any signs of leakage.
• Check the differential fluid level after the test drive to ensure proper fill level is maintained.
• Listen for any unusual noises from the rear axle during the test drive that could indicate improper axle shaft installation.

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