maintenance

Differential Service

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

1.0 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.

This procedure covers draining, inspecting, and refilling the rear differential fluid on a 1970 AMC Rebel Machine with 390ci V8 and rear-wheel drive.

Warnings

⚠Ensure vehicle is securely supported on jack stands before working underneath. Never rely solely on a hydraulic jack.

⚠Differential fluid may be hot if vehicle has recently been driven. Allow adequate cooling time.

ℹ️Some AMC differentials use a limited-slip additive. Check for identification tag on differential cover before servicing.

Tools required

3/8 inch drive ratchetEssential

3/8 inch drive socket set (metric and SAE)Essential

Oil drain pan (minimum 4 quart capacity)Essential

Fluid pump or squeeze bottleEssential

Wire brush

Scraper or gasket removal toolEssential

Jack and jack stands rated for vehicle weightEssential

Wheel chocksEssential

Torque wrenchEssential

Shop rags or towelsEssential

Parts

Differential cover gasket × 1 — Use OEM specification or equivalent
RTV silicone gasket maker (optional alternative to gasket) × 1 — High-temperature rated

Fluids

SAE 80W-90 or 85W-140 gear oil (GL-4 or GL-5 specification) — 2.5 qt

Preparation

Park vehicle on level surface and engage parking brake
Chock front wheels securely
Raise rear of vehicle and support with jack stands under frame or axle housing
Ensure rear axle is cool enough to touch safely
Clean exterior of differential cover to prevent contamination during service

Procedure

1
Remove differential cover bolts
Using appropriate socket, loosen all differential cover bolts in a crisscross pattern. Leave the top two bolts partially threaded to prevent sudden cover separation. The AMC rear axle typically uses 10-12 bolts securing the cover.
2
Drain differential fluid
Position drain pan under differential cover. Carefully pry bottom edge of cover away from housing using scraper to break seal, allowing fluid to drain into pan. Once fluid flow slows, remove remaining bolts and lower cover completely. Inspect drained fluid for metal particles or debris indicating abnormal wear.
3
Inspect differential components
With cover removed, visually inspect ring gear, pinion gear, and spider gears for excessive wear, pitting, or damage. Check for metal shavings on magnetic drain plug if equipped. Look for proper gear tooth contact pattern and bearing condition.
4
Clean differential cover and housing
Remove all old gasket material from both the differential cover and housing mating surfaces using scraper and wire brush. Clean surfaces must be completely free of old gasket, RTV, and debris. Wipe clean with shop rags and ensure no material falls into differential housing.
5
Clean magnetic drain plug
If differential cover has magnetic drain plug, thoroughly clean all metal particles and debris from magnet. This is normal wear material but excessive buildup indicates problems.
6
Install new gasket
Position new differential cover gasket on cover, aligning all bolt holes. Alternatively, apply continuous 1/8 inch bead of RTV silicone to cover flange, circling inside of bolt holes. If using RTV, installation must be completed within product's working time (typically 10-15 minutes).
7
Reinstall differential cover
Carefully position cover with gasket onto differential housing, ensuring proper alignment. Thread all bolts by hand to prevent cross-threading. Tighten bolts in crisscross pattern gradually to approximately 20-25 ft-lbs. Since factory torque specification is not available in database, use conservative torque to avoid warping cover while ensuring adequate seal.
8
Fill differential with gear oil
Locate fill plug on front or side of differential housing (typically 1/2 inch or 5/8 inch square or hex). Remove fill plug. Using fluid pump or squeeze bottle, add gear oil through fill hole until fluid reaches bottom of fill plug hole (fluid should just begin to seep out). For limited-slip differentials, add appropriate limited-slip additive per manufacturer instructions before topping off with gear oil.
9
Reinstall fill plug and check for leaks
Clean fill plug threads and reinstall, tightening securely. Wipe exterior of differential cover and housing clean. Lower vehicle and check for leaks around cover gasket and fill plug after running vehicle briefly.

Reassembly

If RTV was used instead of gasket, allow 24 hours cure time before driving vehicle for best results
Recheck differential cover bolt tightness after first 50-100 miles of driving

Verification

Check for fluid leaks around differential cover gasket after test drive
Verify proper fluid level by confirming fluid reaches fill plug hole
Listen for abnormal noise from rear axle during test drive indicating improper assembly or low fluid level
Monitor for leaks after several days of normal driving

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