Differentials
Spicer 23 Rear Axle
The Spicer 23 rear axle was used in the CJ2a until about 1946.
The Spicer company was later acquired by the Dana Corporation.
The Spicer 23 was the only
full-floating rear axle offered on a CJ from the factory. The Spicer 23 was a weak axle. It is best to swap this axle out in favor of a Dana 44 or almost any other newer axle.
The Spicer 23 axle is 51 inches wide and the spring perches are 28 inches apart.
Dana Spicer 25 Front Axle
The Dana 25 was a front axle available from
1945 to 1966 in Willys CJ2a, CJ3a CJ3b, CJ5, CJ6.
The
ring gear is 7.75 inches in diameter.
This axle was first designed in the late 1930's long before the first CJ was built. Even though the ring gear is 7.75 inches across, it's not a very strong axle and there isn't really any way to upgrade it's strength. Unless you are set on keeping your CJ with all original equipment the Dana 25 is best swapped out in favor of stronger axles. The Dana 25, like all early front axles, used an enclosed steering knuckle.
The Dana 25 is 51 inches wheel to wheel. The spring perches are 28 inches apart.
The Dana 25 used an enclosed steering knuckle with Bendix, Tracta or Rzeppa CV joints.
Tracta CV joint used in earlier Dana 25 axles. As you might imagine, this was a poor design that did not hold up well.
Rzeppa Cv Joint
This early CV joint was an improvement over the Tracta but still not as durable as the cardan U-Joint of later axles.
Dana Spicer 27 Front Axle
The Dana Spicer 27 front axle was available from
1961 to 1971 in CJ3b, CJ5, CJ6.
The
ring gear is 7 1/8 inches across.
The Dana 27 is 51 inches wide wheel to wheel. The spring perches are 28 inches apart.
The Dana Spicer 27 was based on the Dana 25. It is slightly smaller but slightly stronger than the 25.
The Dana 27, like the Dana 25 used enclosed steering knuckles but the Dana 27 used a cardan u-joint that was much better than the CV joints of earlier axles.
The seal on the enclosed steering knuckle was often a problem.
Dana Spicer 30 Front Axle
The Dana 30 front axle was available from
1972 to 1986 in CJ5, CJ6. CJ7, CJ8.
The
ring gear is 7 1/8 inches across.
The Dana Spicer 30 was based on the Dana 27 but had 2 more ring gear bolts even though the ring gear diameter was the same. The Dana 30 used in the CJ has 27 splines. Limited slip was not an option from the factory but there are lots of after-market options.
The narrow track axles were used from '72 to '81. They had a width of 53 inches from wheel mating surface to wheel mating surface. In 1982 AMC changed the axles to “wide track” to make the CJ more stable. The wide track axles were 56 inches from WMS to WMS. The spring perches were always 27.5 inches apart irregardless of if it was wide or narrow track.
The Dana 30 front axle originally came with 11 inch drums. In '77 disk brakes became standard.
Up to 1980 the locking hubs were held on with 6 bolts. After that CJs came with a weaker hubs that were held on with 5 bolts. Either design had issues with the bolts coming loose. The factory dealt with this by supplying tabs that bend over to keep the bolts from coming loose. Without these tabs I find that even red (non-removeable) thread lock will only hold these bolts for a year before they start to come loose. If your CJ no longer has the factory locking tabs another common option it to use studs in the hubs and then nuts on each stud. I don't know why this works so much better than bolts but the nuts are much less likely to come loose.
The steering knuckles of a newer CJ can be installed on an older Dana 30 axle. This can be done to upgrade to disk brakes.
The Dana 30, like all CJ axles used a 5 x 5.5 bolt pattern.
Dana Spicer 41 Rear Axle
The Dana 41 rear axle was available from
1946 to 1949 in the CJ2a and the CJ3a. It had a
7.75 inch ring gear.
The Dana 41 axle was 51 inches from wheel mating surface to wheel mating surface. The spring perches are 28 inches apart. The Dana 41 has 10 spline axles.
Parts are very hard to find. If you are having trouble with a Dana 41 axle you are best off upgrading to a Dana 44.
The Dana 41 was used as the basis of the Dana 44.
Dana Spicer 44 Rear Axle
The Dana 44 rear axle was available from
1949 to 1986 in the CJ3a, CJ5, CJ7, CJ8. The Dana 44 was standard in CJs up to 1975. From that year on the AMC 20 was standard but the Dana 44 sometimes came in the rear of CJs as a heavy duty axle. 1986 was one year that AMC often used the Dana 44 rear axles as the AMC 20 was in short supply.
The Dana 44 has a
8.5 inch ring gear.
If you replace the differential in a Dana 44 axle make sure to get the correct spline count.
In the '50s the Dana 44 had 10 splines on the inner end of the axle shaft. These axles had a two piece axle and the differential was offset to the passenger side because the Dana 18 transfer case was in use.
In the '60s there was 19 splines on the inner end. The axle shafts were flanged and the differential was still off-set.
In the '70s the Dana 44 had 30 splines on the inner end of the axle shafts. These axles had a one piece flanged axle shaft. In 1972 Jeep CJs started to come equipped with the Dana 20 transfer case and for that reason the differential had to be centered.
AMC 20 Rear Axle
Easy to identify because of the very round differential cover
The AMC 20 rear axle (sometimes called the Corporate 20) was available from
1976 to 1986 in the CJ5, CJ7 and CJ8.
The AMC 20 has a
8 7/8 inch ring gear.
All AMC 20 axle shafts have 29 splines.
When AMC bought the Jeep company the decision was made to replace the Dana 44 axle with the AMC 20 rear end. This corporate decision was made for obvious reasons. It is less expensive to sell your own axles than re-selling someone else's. The AMC 20 axle was used in passenger cars and muscle cars since '68. This axle worked out fine for the passenger cars. The AMC 20 has a bigger ring gear than the Dana 44. You would think it would work out fine for the Jeeps. Unfortunately the off-road crowd was much less impressed with the AMC 20. There are several problems with the AMC 20. Most importantly was the 2 piece axle design. A hub fit onto the end of the axle shaft. A splines and woodruff key were used to keep the hub from rotating. Then the hub was held on with a large nut on the end of the axle. It was a common problem that the axle shaft would spin in the hub.
If you have an AMC 20 rear end it is recommended to upgrade the axle shafts. A one piece axle kit is the most common upgrade for this axle. Both Moser and Superior make one piece axles for the AMC 20. The Superior axle kit is also marketed and sold under other names.
Both Warn and Summers Brothers have made full-floating kits for the AMC 20 rear end. Neither of these kits are available any more.
Although the two piece axle shaft was the biggest problem with the AMC 20, another weakness was where the axle tubes fit into the pumpkin. If you plan on working your CJ hard off road you could weld the axle tubes here or better yet add an axle brace. The axle tubes are smaller than the Dana 44 tubes. Also the axle shafts are smaller too.
Narrow Track & Wide Track
The narrow track axles were used from '72 to '81. They had a width of 53 inches from wheel mating surface to wheel mating surface. In 1982 AMC changed the axles to “wide track” to make the CJ more stable. The wide track axles were 56 inches from WMS to WMS. The spring perch was always 27.5 inches apart.
