2000 XJ np231 Transfer Case Issues

Several months ago, my Jeep started making a loud grinding noise at speed. I narrowed the issue down to the transfercase where I discovered it was low on fluid. I topped it back up and continued where it was fine for a few days before the noise came back. I checked the transfercase again and sure enough, it was low on fluid.

I cleaned it off with brakeklean to see if I could find where it was coming from. The next morning I found it completely saturated again. It almost appeared as though the seal had gone bad which caused it to start leaking.

I continued this game of adding fluid due to not having the funds to fix it at the time until I found a large crack pushing from the inside out had developed where the transfercase would no longer hold any fluid. I finally was able to pull a used one from my local yard. I put together some JB and patched it enough to fill it and drive it over to my mechanic.

Fast forward a few days and the new case was in. However, when driving it in 2wd, it makes a similar loud grinding sound but only if the wheels are touching the ground. Meaning, if you jack the rear end up and have the tires spin freely, you cant hear anything but when driving normally, it gets quite loud. When you slip it into 4hi or lo, it continues to make noise and disengages when trying to apply power.

This lead me to believe I just so happened to pickup a bad unit however now, when looking at purchasing another replacement one thing I didnt take into account was the spline of what I had and what was going into it.

If memory serves me correctly, the donor came out of a 98 XJ to replace the one in my 00 XJ. I confirmed both models as NP231 but could the spline be different?

Is there anything else that I could check before just biting the bullet and buying a remanufactured unit?

Many thanks. I quite miss driving the Jeep around even though my Golf TDI gets much better mileage.

98 to 00 is fine. Any 96 or later NP231 should be 100% bolt-in. You may have to swap the VSS and/or VSS drive gear but that is a small bolt or two, easy, just make sure you properly engage the drive gear teeth or it will strip out quickly (it's just plastic.)

I'd try your luck with another junkyard unit, or disassemble and inspect the current one. There should be no roughness in the bearings and no slack in the chain (can be checked with a finger through the fill or drain plug hole, iirc.)

Replacing one yourself isn't too bad, 6 bolts hold it to the tranny, plus the linkage, cables, driveshafts, and crossmember.

Thanks for the reply.

Not sure what you mean by VSS? I'm pretty good mechanically I'm just not familiar with what you're referencing.

I've been considering doing the 2nd swap myself no matter what option I go with. The only challenge I had when I first pulled the donor from the junkyard was disconnecting it from the tranny. The haynes manual really didnt offer too much insight in that regard which kind of sucked but I wouldnt mind tackling the project as it's no longer my primary means of transportation and is just sitting in my driveway at the moment.

I'm also starting to think I may need a new rear main as I have another leak that has developed since all this started.

VSS - vehicle speed sensor. It's the one mounted to the tailcone.

Yeah, the toughest part is disconnecting it from the tranny... the bolt at the top is difficult if it's in a vehicle, and the bolt hidden behind the shift linkage mount plate is difficult no matter where it is (whose stupid idea was that anyways? next time I do that, I'm taking a Dremel to it and making it easier on myself.) Pretty simple otherwise.

People sometimes have the bolts from the crossmember into the frame break off or seize, I personally haven't had that issue even on my ultra rusty rigs (the 91 and 96.) Yours have already been off once so unless the shop that did the swap last time did a horrible bodgy job on it, they should come out easily again.