This is the ever-popular Spicer...
This is the ever-popular Spicer 18 transfer case, specifically the less-desirable early WWII version with a 1.96:1 low range and a smaller 3/4-inch intermediate shaft. Later models had 2.46:1 gears and either a 11/8- or 11/4-inch shaft. All have both the front and rear output shafts on the righthand side.
In 1988, Jeep began using...
In 1988, Jeep began using the super-popular NP231 made by New Process in YJ, XJ, and six-cylinder ZJ models. The NP231 has a 2.72:1 low range and, unlike the all-gear Spicer 18 and Dana 20 cases, used a chain to link the two output shafts together and a planetary gearset to provide gear reduction.
The Dana 20 started phasing...
The Dana 20 started phasing out the Spicer 18 with its introduction in 1963. However, Jeep would continue to use both cases until 1971. The Dana 20 has a righthand front output and a centered rear output. Unlike the 2.46:1 low range of the Ford Dana 20s, the Jeep versions had a 2.03:1 low range, although the Ford gears can be swapped.
Theres about as much science involved in dissecting which transfer cases were offered in Jeep vehicles over the years as there is in swinging a dead cat over your head under a full moon. Its not that difficult to determine which transfer case your heep came with or which one may prove good for swapping, as long as you know what to look for.
Weve listed some of the more popular T-cases below and the options you have when swapping. Its up to you to decide which case you have and which you feel may be better for your application or intended use. You can go either waystick with what youve got or swap to something else if thats what floats your boat.