drivetrain

Differential Cover Gasket

for 1970 AMC Rebel Machine 390ci V8 · RWD

Editorial review:Chris Hackleman — Master Technician · 20+ years · Jeff Moore — Master Lexus & Toyota Mechanic · 20+ years

Difficulty

Easy

Time

1.5 h

Tools

Steps

✓Expert-verified. Personally reviewed and approved by OLP's master technicians (Chris Hackleman & Jeff Moore — 20+ years each). Always follow the vehicle's factory service information and torque specs.

Replace the differential cover gasket on the rear axle assembly to prevent gear oil leaks.

Warnings

⚠Vehicle must be supported on jack stands, never work under a vehicle supported only by a jack

⚠Gear oil can be extremely slippery; use appropriate containment and clean spills immediately

ℹ️The 1970 AMC Rebel Machine may have either a Dana 44 or AMC 20 rear axle; verify which axle you have before ordering parts

ℹ️Allow the differential to cool completely before draining if the vehicle was recently driven

Tools required

Jack and jack stands (rated for vehicle weight)Essential

Wheel chocksEssential

1/2 inch drive ratchet and socket setEssential

3/8 inch drive ratchet and socket setEssential

Drain pan (minimum 4 quart capacity)Essential

Gasket scraper or plastic scraperEssential

Brake cleaner or degreaser

Shop ragsEssential

Wire brush

Torque wrench

Rubber mallet

RTV silicone sealant

Parts

Differential cover gasket × 1 — AMC Dana 44 or AMC 20 rear axle gasket (verify axle type)

Fluids

SAE 80W-90 GL-5 gear oil — 4 qt

Preparation

Park vehicle on level surface and apply parking brake firmly
Place wheel chocks in front of front wheels
Raise rear of vehicle and support securely on jack stands at the frame rails or rear axle housing
Verify rear wheels are off the ground and vehicle is stable
Identify differential type (Dana 44 or AMC 20) by inspecting cover shape and bolt pattern

Procedure

1
Position drain pan
Place the drain pan directly underneath the differential cover to catch all draining gear oil. Position it slightly forward of the cover as oil will flow toward the front when bolts are removed.
2
Loosen differential cover bolts
Using the appropriate socket, loosen all differential cover bolts in a crisscross pattern, but do not fully remove them yet. Start at the top bolts and work down, leaving the upper bolts slightly tighter than the lower ones.
3
Drain gear oil
Remove the lower bolts first to allow the cover to tilt and gear oil to drain. As oil drains, continue removing bolts working from bottom to top. Remove all bolts except the top two, allowing the cover to hang and drain completely. This may take several minutes.
4
Remove differential cover
Once oil has completely drained, remove the final two bolts and carefully remove the differential cover. You may need to gently tap the cover with a rubber mallet to break the gasket seal. Pull the cover straight out to avoid damaging the ring gear.
5
Clean cover and housing surfaces
Using a gasket scraper, carefully remove all old gasket material from both the differential cover and the axle housing mating surface. Be thorough but gentle to avoid gouging the metal surfaces. Use a wire brush and brake cleaner to remove any remaining residue and oil. Wipe both surfaces completely clean and dry with shop rags.
6
Inspect differential internals
With the cover removed, visually inspect the ring gear, pinion gear, and carrier bearings for any unusual wear, metal shavings, or damage. Check the magnetic drain plug (if equipped) for excessive metal particles. Minor fine particles are normal, but large chunks or excessive material indicate a problem.
7
Install new gasket
Position the new differential cover gasket on the axle housing, aligning all bolt holes. Some gaskets are directional; verify proper orientation. A thin bead of RTV silicone sealant on both sides of the gasket can help prevent future leaks, though this is optional with quality gaskets.
8
Install differential cover
Carefully position the differential cover against the gasket, ensuring the gasket remains properly aligned. Start all bolts by hand, threading them in a few turns to hold the cover in place. Do not force any bolts; they should thread easily if the gasket is properly aligned.
9
Tighten cover bolts
Tighten the differential cover bolts in a crisscross star pattern, working from the center outward. Tighten in three stages: first snug all bolts finger-tight, then tighten to approximately 15-20 ft-lbs, and finally to 25-30 ft-lbs. This ensures even gasket compression and prevents warping the cover.
10
Refill differential with gear oil
Locate the differential fill plug on the front or side of the axle housing. Remove the fill plug and add SAE 80W-90 GL-5 gear oil until it begins to drip from the fill hole. The differential is full when oil reaches the bottom of the fill hole threads. Reinstall and tighten the fill plug securely.
11
Lower vehicle and test
Remove jack stands and carefully lower the vehicle to the ground. Start the engine and allow it to idle in park. Cycle the transmission through all gears while stopped, then drive the vehicle forward and reverse a few feet to circulate the new gear oil through the differential.

Reassembly

Ensure all differential cover bolts are tightened in proper sequence to prevent gasket leaks
Verify fill plug is securely tightened after filling with gear oil
Double-check that drain pan and all tools are removed from under vehicle before lowering

Verification

Check for any gear oil leaks around the differential cover gasket while the vehicle is idling
After a short test drive, re-inspect the differential cover for any signs of seepage
Check the area under the vehicle after it has sat overnight to confirm no leaks are present
Verify proper gear oil level at the fill plug after initial operation

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