You can spend thousands of dollars replacing your OEM differentials with larger aftermarket differentials or you can save some money by beefing up what you already have. From the mid ‘70s to the mid ‘80s, Jeep CJ models have been equipped with Dana 30 front differentials and AMC 20 rear differentials; Jeep is still using the Dana 30 on Wranglers today, so my information is still valid. If you follow my advice, your OEM axles can survive for years of fun four-wheeling!

AMC 20
The AMC 20’s ring and pinion are actually 3/8-inch larger than the Dana 44, but the AMC 20 uses smaller diameter axle shafts, smaller axle tubes, and comes with weaker two-piece axle shafts. It uses a 29-spline axle shaft whereas the later Dana 44 uses a 30-spline axle shaft (Jeep started using 44s in late-1986 CJ-7 models). As I said above, the AMC 20 has two major flaws: thin weak axle housings and two-piece axles.

The weak housing can flex and bend (I’ve actually had one of the original AMC 20 axle tubes on my ’82 CJ-7 bend upward at the spring plate, causing the wheel to rub on the inside fender). The reason the AMC 20 can flex more than the Dana 44 is its more narrow differential housing and thinner, smaller diameter axle tubes. This design can allow bending of the housing tubes and/or breakage to the axle shafts. However, this can be remedied by adding gussets and/or welding the tubes to the differential housing. Its other flaw is the two-piece axle made up of a hub and a shaft. The hub end tends to break off and/or spin on the shaft under load.

The breaking strength of an OEM AMC 20 axle shaft is about 90,000 pounds, which does not take into consideration any problems with the hub attachment to the shaft, or the strength of the Wentworth key that holds it in place. The breaking strength of most one-piece axles (Summers Brothers, Moser, Superior, etc.) is about 125,000 to 135,000 pounds, and I’ve been told that the breaking strength of the shafts in the Warn full-floater axle kit, which is what I have in my 1982 CJ-7, is about 230,000 pounds.

Unfortunately, my Warn full-floater kit was installed more than 15 years ago so I have no photos of the install, and as I understand it, the complete full-floater axle kit (designs, patents, etc.) was sold to Randy’s Ring & Pinion and is no longer available (although Randy’s does have free-wheeling hubs for the kit if you already have one). Suffice it to say, if you wish your AMC 20 to survive a difficult rocky, technical trail, you need to replace the two-piece axles with one-piece shafts (there are several manufacturers offering them, with excellent installation instructions), weld up the axle tubes, weld on a full-width gusset, and I’d suggest a locker as well.

The AMC 20 was introduced to American Motors’ Jeeps in 1976, the same year the CJ-7 was introduced. CJs were equipped with two versions of the AMC 20: 1976-’81 had the narrow track and the wide track was on the ‘82-’86 models. Both AMC 20 versions use the keyed, two-piece shaft/hub design and a five-by-5.5-inch wheel bolt pattern. As noted above, supplies of AMC 20s were exhausted in 1986 and some Dana 44s were used instead in the last of the CJ-7s. Author’s note: In 1976-1978 larger 11x2-inch drum brakes were used on the AMC 20; a 10x1.75-inch drum was used after 1978.

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