This adapter kit will allow you to adapt the GM SM420 4 speed manual transmission to the Jeep 231 transfer cases with a 21 spline input shaft. The adapter is 5.250” in length and is made from strong 356 T-6 heat treated aluminum alloy. We also supply a mounting provision on the bottom of the housing to use our heavy duty transmission mount (716008).
The adapter kit includes a adapter housing, spud shaft, snap ring, set collar, gaskets, seal, fastening hardware, and adapter instructions.
Note: The NP231 must have a 21 spline input shaft with a stickout measurement of 1.19”
The adapter assembly will fit the Jeep NP231 transfer case with a 21spline input shaft. Introduced in 1988, the Jeep NP231 is a part-time transfer case became the standard for XJ and YJ models. It was also used in six cylinder ZJ models through 1995. Chain driven with a 2.72:1 low range, it’s reliable even with more than stock horsepower applied.
The kit is designed for exclusive use with the GM SM420 4 speed transmission. The SM420 was used in GM trucks 1947 to 1968 and has a 10 spline output shaft and was used in both 2wd and “divorced” 4wd applications. The large case iron case with a large bulge on the passenger side makes it easy to identify.