It's no secret; '76-'86 CJs are ugly. Big bulbous fenders, tacky grilles, and a body style that had been pretty much the same for over 30 years. Some owners have grossly disfigured their Jeeps even more by bathing the leper-like body in horrible colors of purple, pink, and other Easter pastels. But we're not going to chastise anyone for that (at least not more than we already have). What we will do is let you in on some buildup tips--things that need attention and things to look for on the final round fenders.
The '76-'86 Jeeps began life with some less-than-durable components. Almost all of them were outfitted with AMC model 20 rearends. This is probably the worst axle in Jeep history. The two-piece shafts are prone to breakage and the centersection has been known to spin on the axletubes. The tubes themselves are small in diameter, have thin tubing, and are easy to bend, even with 31s. For all of these reasons it is best to replace the 20 with a stouter unit such as a Dana 44. Some '86 CJs came with Dana 44 rear axles. These are hard to find in wrecking yards so a custom unit may be your only hope. Beware: Narrow-track CJs ran from 1976 until around 1982. The axles in these Jeeps are about 3 inches narrower than the later models. On top of this problem is that AMC 20s came with all kinds of different axleshaft lengths (up to 1/2-inch difference), even on models of the same year. This often makes the installation of aftermarket axles and full-floaters a pain. If the housing is bent the new axles will usually leak oil or screwup the locking hubs on a full-floater. In other words, ditch the AMC 20.
A standard-rotation Dana 30 can be found in the front. Anything bigger than 33-inch-tall tires and the 30 will most likely scatter if abused regularly. The smallish 260 U-joints are the weak link. Heavy-duty shafts with 297 joints help, but the housing, gears, and 27-spline shafts are much happier with smaller tires.
During this time period the CJ came with three different transfer cases. The Dana 20 (1972-1979) the Borg-Warner 1305 Quadra-Trac (1976-1979) and the revered Dana 300 (1980-1986). The full-time 1305 is perhaps one of the most bad-mouthed transfer cases that ever came in a Jeep, but it is a respectable unit if it is serviced properly. It is a chaindrive splitter with an admirable low range of 2.57:1. Case failure is common if the chain fails from lack of, or use of, an incorrect lubricant. The Dana 20 is a part-time, geardriven 'case with a comparatively sad low-range of 2.03:1. With the exception of the factory low range it is a good transfer case. Companies such as Tera Low offer lower ratios for the 20. The survival of these gears has been debatable in some applications. The Dana 300 is also a part-time, geardriven T-case but it has a low range of 2.62:1. Lower gears are also available for the 300. The tailshaft in the 300 has been known to let loose if abused. Advance Adapters offers a 32-spline unit to cure this ailment in the 300.
The transmissions in these Jeeps have been problematic, even behind a choked-down inline-six. The exception is the Borg-Warner T-18 that was available from 1976 to 1979 behind the six-banger. Some dealers would swap in V-8s retaining the T-18, but this was never available from the factory. All of the other transmissions (T150, T176, SR-4, T5, and T4) are marginal, even though adapters are available to mate them to various V-8s. The T-18 is a truck-type transmission with a granny-low First gear. The low First gear is a plus in rocky, slow-going terrain. Other areas that require tire speed can also benefit from the strength of the T-18, even if the First gear is not used often. CJs equipped with Quadra-Trac transfer cases came with an AMC version of the GM TH400. Other autos available were the TorqueFlite 904 and 999. The 904 was available behind the Iron Duke 151. This engine has the same bolt pattern as a Chevy. However, bolting in a small-block is not as easy as it seems. Here are some other tips for building up your CJ. If you're not sure what size tire fits with what lift, we also made a chart that will help.