AMC 20 Rear Axle Identification and Parts

The AMC Model 20 is the rear axle most people mean when they search for a Jeep CJ regear. It was standard in 1976–1986 CJ-5, CJ-7, and CJ-8, and it also showed up under AMC cars, J-Series trucks, Wagoneers, and Hummer H1s. The housing is stout enough for trail use, but the factory two-piece axle shafts are the weak link. Most builds start with one-piece shafts, then add ring and pinion, an installation kit, and a locker or limited slip.

How to identify an AMC 20

Pop the cover or count bolts from underneath. The Model 20 is one of the easier axles to ID:

• 12 cover bolts — the quickest visual check
• 8.875" ring gear on (8) 7/16"–20 ring-gear bolts
• 1.625" pinion with 28 splines
• Carrier break: 2.73/2.76 and numerically lower vs. 3.07 and numerically higher

If you are swapping ratios, match the carrier to that break. A 3.73, 4.11, 4.56, or 4.88 set uses the 3.07-and-up carrier that most CJ axles already have.

Gear ratios

We stock AMC 20 ring and pinion in 3.08, 3.31, 3.54, 3.73, 4.11, 4.56, and 4.88. Milder ratios (3.54–3.73) suit mixed street driving with stock or 31" tires. 4.11 is the usual all-around pick for 31–33" tires. 4.56 and 4.88 restore crawl and low-end torque after a lift or larger tires. Use a master installation kit (bearings, shims, crush sleeve, pinion seal) whenever the pinion comes out.

Common upgrades

The two-piece factory shafts are the first thing to fail on a CJ used off-road. Convert to one-piece shafts before you add a locker. Then pick a traction device that matches how you drive: an automatic locker for trails, a helical limited slip for mixed street use, or a spool for a dedicated off-road rig. Pair the locker with fresh bearings and the correct gear ratio so the housing is not the next weak point.

Vehicle applications

The AMC 20 was commonly found on:

• 1968–1970 AMX, rear
• 1976–1983 Jeep CJ-5, rear
• 1976–1986 Jeep CJ-7, rear
• 1981–1986 Jeep CJ-8, rear
• 1978–1979 AMC Concord, rear
• 1992–2006 Hummer H1, front
• 1992–2006 Hummer H1, rear
• 1970–1977 AMC Hornet, rear
• 1976–1986 Jeep J10, rear
• 1967–1974 AMC Javelin, rear
• 1971–1978 AMC Matador, rear
• 1975–1980 AMC Pacer, rear
• 1979–1986 Jeep Wagoneer, rear