This procedure drains and refills the rear differential fluid on a 1970 AMC Rebel Machine to maintain proper lubrication and prevent premature wear of the ring and pinion gears.

Warnings

Tools required

Parts

• Differential cover gasket × 1 — AMC 20 or AMC 15 rear axle cover gasket depending on axle code
• RTV silicone sealant × 1 — High-temp anaerobic gasket maker as alternative

Fluids

• 80W-90 or 85W-140 Gear Oil (GL-4 or GL-5) — 4 qt

Preparation

1. Park vehicle on level ground and engage parking brake
2. Allow differential to cool completely if recently driven
3. Chock front wheels securely
4. Raise rear of vehicle with floor jack at rear axle housing or frame contact points
5. Support vehicle securely on jack stands placed under frame rails
6. Verify vehicle is stable before working underneath

Procedure

1. 1

   Locate and inspect differential cover
   Position yourself under the rear axle and locate the differential cover on the rear of the axle housing. Inspect for existing leaks, damage, or stripped bolt holes. The cover is typically oval-shaped with 10 bolts around the perimeter. Note the axle identification tag if present on one of the cover bolts.
2. 2

   Position drain pan
   Place a drain pan with at least 4 quart capacity directly beneath the differential cover. Position it slightly toward the bottom of the cover where fluid will drain most heavily when the cover is removed.
3. 3

   Loosen differential cover bolts
   Using a 1/2 inch drive ratchet with appropriate socket (typically 1/2 inch or 9/16 inch), loosen all cover bolts in a crisscross pattern, but do not remove them completely. Loosen the top bolts first, leaving the bottom bolts slightly tighter to control fluid drainage.
4. 4

   Remove upper cover bolts and break seal
   Remove the upper cover bolts completely. Carefully loosen and remove the bottom bolts while maintaining upward pressure on the cover to control fluid flow. Once the seal breaks, gear oil will begin draining. Allow the cover to tilt down gradually to control the drainage rate. Remove all bolts and carefully lower the cover, allowing all fluid to drain into the pan.
5. 5

   Remove and clean differential cover
   Once fluid has drained completely, remove the cover and set aside. Use a wire brush and shop rags to clean the interior of the cover. Inspect for metal shavings or debris. A small amount of fine metallic paste on the magnetic drain plug (if equipped) is normal; large metal chunks or excessive debris indicate internal wear problems.
6. 6

   Clean gasket mating surfaces
   Using a gasket scraper and wire brush, thoroughly clean the gasket mating surface on both the differential housing and the cover. Remove all traces of old gasket material and RTV sealant. Wipe surfaces clean with shop rags. The mating surfaces must be completely clean and dry for proper sealing.
7. 7

   Inspect differential internals
   With the cover removed, visually inspect the ring gear and differential components for visible damage, excessive wear, or metal debris. Check that the ring gear teeth appear intact and the backlash seems normal. This is not a complete inspection but can reveal obvious problems.
8. 8

   Install new gasket and prepare cover
   Place the new differential cover gasket onto the cover, aligning all bolt holes. Alternatively, if using RTV sealant instead of a gasket, apply a continuous 1/8 inch bead around the inside of the bolt holes on the cover. If your differential has a magnetic drain plug in the cover, ensure it is clean and reinstalled.
9. 9

   Reinstall differential cover
   Carefully position the cover with gasket onto the differential housing, aligning all bolt holes. Start all bolts by hand to ensure proper thread engagement. If using RTV without a gasket, install the cover within 5 minutes of applying sealant. Tighten bolts in a crisscross pattern in three stages: first snug by hand, then to half torque, then to final torque of 20-25 ft-lbs. Do not overtighten as this can distort the cover and cause leaks.
10. 10

    Locate fill plug
    Locate the fill plug on the front of the differential housing. It is typically a 3/8 inch square drive plug located on the passenger side of the housing near the top. Clean area around the fill plug before removal.
11. 11

    Remove fill plug and add gear oil
    Using a 3/8 inch drive ratchet or square drive, remove the fill plug. Using a fluid pump or squeeze bottle with appropriate nozzle, add gear oil through the fill hole. Fill until oil begins to seep out of the fill hole opening. The proper fill level is at the bottom of the fill plug hole. If equipped with limited slip differential, add appropriate limited slip additive per the additive manufacturer's instructions.
12. 12

    Reinstall fill plug
    Once fluid reaches the proper level (beginning to drip from fill hole), reinstall the fill plug. Tighten the fill plug to 25-30 ft-lbs. Wipe away any spilled gear oil from the differential housing.
13. 13

    Lower vehicle and check for leaks
    Remove jack stands and carefully lower the vehicle to the ground. Start the engine and allow it to reach operating temperature. With the engine running and parking brake engaged, shift through all gears. Drive the vehicle forward and reverse a short distance to circulate the new fluid. Immediately check for leaks around the differential cover and fill plug.

Reassembly

1. If RTV sealant was used instead of a gasket, allow 1 hour cure time before filling and 24 hours before driving to ensure proper seal
2. Dispose of used gear oil properly at a recycling center or auto parts store that accepts used oil

Verification

• Check differential cover for any signs of leakage after test drive
• Verify fill plug is secure and not leaking
• Confirm smooth operation with no unusual noises from rear axle during test drive
• Recheck fluid level after test drive by briefly removing fill plug - fluid should be at the bottom edge of the fill hole

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