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Differences In 231 One Cases

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Ok so I'm getting ready to set up dual doubles what ever you want to call them... I'm gunna run two np 231s I found another 231 out of what my buddy says came out of a 4cylinder 93 Cherokee so my question is does that mean its different than a 6cylinder truck bc different tranny's ?? and are all interchangeable? And all 91 and new tcase are all 23 spline as far as I know ?


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All 231s behind the AX4 or Ax5 (4 cylinder manual transmissions) were 21 spline regardles of year. But worse, both for 21 spline and 23 spline there are three different length input shafts. Not only do you need to correct spline count for your transmission, you also need to correct length.


Right around 94 they changed a few things inside the case. One difference is that it will have a true neutral, whereas the older ones in neutral lock the front and rear output shafts together. Another difference is the cur of the gears. Because of that input shafts can be swapped between older ones, or they can be swapped between newer ones. But an older input shafts will not work in a newer case, nor will a newer input shaft work in an older case.

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I have a 94 tcase right now but the other one is a 93 out of a 4 cylinder idk which tranny it had behind it tho

 I know both the AX4 and AX5 use the same input shaft since they are basically the same transmission. The AX4 is just missing the gears and shift rail for 5th gear. Don't know what an automatic transmission behind a 4 cylinder got, but those are few and far between.

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Half a 231 (just the gear reduction housing) between the transmission and whole transfer case.


high 2wd = normal 2wd

low 2wd = low range 2wd (not available with just one case)

high 4high = normal 4wd

high 4low = 2.72 low range 4wd

low 4 high = 2.72 low range 4wd

low 4low = 7.40 super low range 4wd (not available with just one case)


Now if you install a terra-low kit in one of them, your available ratios will be 





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From what i understand usually the aluminum case explodes.


You figure the torque of the engine is multiplied by your transmission then again in the t case, a 231 is only rated for 1885lbs max torque which should be way less then what's gonna be coming out of the first case in low range.

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