Transfer Case replacement 99 XJ

I have to replace the TC in my 99 XJ. I have a few questions before I embark on this task!

1) Will all NP231s swap out? I've found a used one on CL out of a 4cyl YJ for a good price.

2) How hard is it going to be? I'm more of an library book mechanic but I'm pretty comfortable with tools.


Any other advice would be very much appreciated!!

I believe the YJ 231 is clocked differently. Not sure.

How hard - jack up transmission with scissor/bottle/whatever jack, remove transfer case crossmember, disconnect driveshafts, remove shift linkage (hardest part IMO), lower transmission and transfer case a few inches, remove top nut holding transfer case onto tailhousing adapter, remove other 5 nuts. One hides behind/under the rubber transmission mount. Swap transfer case out, bolt back in, reinstall other hardware, adjust shift linkage, done.

EDIT: a 90 or earlier TC will NOT swap in due to the input shaft being 21 spline instead of 23, you can swap the gear if you want but it's not as easy and 21 spline ones are rarer anyways. A 96 or later TC will be an exact swap though you may need to swap your VSS and/or 4WD sense switch over to get the right connector and whatnot. A 91 through ?? (92? 93?) TC will be vac disconnect and you'll need to swap the 4WD sense switch and probably VSS. A ?? through 95 TC will be close to exact, swap the VSS and maybe 4WD sense switch and you'll need a different rear driveshaft setup (or a very clean yoke iirc) to get the tailhousing right without it leaking. I'd aim for a 96 up case, myself, they're the closest to drop-in and are more likely to be low mileage anyways.

I believe that the 4cyl, and the 1987-1990 6cyl have 21 spline input shafts, and the 1991+ 6cyl have 23 spline input shafts. I'm not sure about the speedo applications though.

I don't believe spline count is engine dependent, though I am not sure. Also AFAIK, 90s can be either 21 spline (early 90s) or 23 spline (late 90s) so you really have to pull it apart and count.

the new body styles(97+) and the old body styles(95-) use different main shaft lengths and different tail shaft housings, so you can put in the older case but might have to get the driveshaft with it. THe newer 231j's(97+) use a 1 piece tailshaft housing that the yoke does not penetrate, and being that it is 1 piece it is shorter than the 2 piece housing of old. People always talk about driveline vibes being worse in the newer ones, this is some of the reason. The older 2 piece housings are penetrated by the yoke and there is a bearing inside that keeps the yoke from wobbling, so if your lifted odds are less chance of vibs with older case.

THe speedo sensor should just straight swap across