View Full Version : NP231 transfer case rear seal replacement

August 4th, 2007, 11:52
My '92 XJ I6 autotranny has an NP231 transfer case. It just began leaking a drop or two of tranny fluid from the point where the rear drive shaft exits.

Is replacing this seal difficult?
Any write-ups?
Where can I buy the seal?


August 26th, 2007, 10:23
Anybody done this? Surely there's some info...?

August 26th, 2007, 10:24
It should be able to be baught at any parts store. It shouldnt be hard to replace.

December 21st, 2007, 07:48
I did this about a year ago... just need to remove the 4 bolts on each side of the shaft... then there is a large bolt that needs to be removed. You need to work the old seal out using a needle nose or reg. pliers, or both. I do not know if I put on the wrong seal, or if I just installed it wrong, but a year later, the leak is back :( I bought the seal from jeep4x4center.com. i think it was $17. Good luck w/ it!

December 22nd, 2007, 11:39
Its VERY easy.

1. Pull the rear driveshaft.
2. Remove the seal. I used a seal puller, but you could use a screwdriver or small flat tool around the edge to pull it.
3. Re-install seal. I HIGHLY recommend a seal installer, it makes it much eaiser to pop that thing back in. I used a block of wood the first time, but I bought a seal installer from Harbor Freight MUCH better.
4. Re-install the driveshaft.

That's it.

I believe it cost me about $15 or less than that.

December 22nd, 2007, 12:01
Lube it with some vasoline or oil before sticking it back on.

December 22nd, 2007, 12:45
1) Remove driveshaft. It's a good idea to have new straps and screws for reinstallation, but get new screws at the very least (should be able to use 1/4"-28 x 1" socket head capscrews - that's what I use. They're cheap insurance, and socket heads have a reduced head to fit, wrench internally, and are heat-treated to SAE8 specs anyhow.)

2) Remove seal. A seal puller would help, but a flat screwdriver will also do the job.

3) Clean the seal seat. A little carburettor cleaner and a clean rag should be enough - you just don't want anything in there that will gouge the aluminum.

4) Install the new seal. Since the output sticks out just slightly, you might find it useful to use a small bit of pipe or a pipe fitting (either with a plug in the end) or a large socket to press the seal rim all at once. Make sure that whatever you use bears on the metal part of the seal! No, I don't recall what size you'll need... Tap gently with a hammer until the seal is fully seated, and I find it useful to smear a bit of RTV Black over the outside of the seal - where metal seats against metal (again, cheap insurance.)

5) Inspect the slip yoke, and clean if necessary. I'll usually give it a pass with some 400-grit emery cloth, just for cheap insurance. Wrap it around the sealing surface, and turn a couple of times. This removes surface rust and other yock. Wipe clean with carburettor cleaner and a clean rag again to remove grit that could compromise the seal.

6) Lightly grease the slip yoke and install.

7) Reinstall the aft end of the driveshaft, using new screws (at a minimum!) and new straps (a good idea.) Use LocTite 242 on the screws to hold them in place - few things are more purely irritating than losing a driveshaft at speed...

Since you'll have the driveshaft out, this is a good time to think about changing the U-joints as well - since half of the job is already done... In any case, get out your grease gun and lube everything while you're down there - five U-joints in the two driveshafts, the two U-joints behind the wheels, the ball joints, and all the tie rod ends and such. Gives you a good chance to check it all anyhow.

The job itself is simple - if you take an hour to do it - with lubricating everything - I'd be surprised. Add a half-hour if you have to change the two universal joints in the rear driveshaft (which probably need it anyhow.) This is also a good opportunity to change the fluid in your transfer case, since you'll lose some anyhow. Dexron II/IIE/III will work - same stuff you'd use in the AW4 (your automatic.)

July 21st, 2014, 06:49
Old thread resurrection.

Other write ups include removal of the tail cone. Is this seal replaceable from the exterior without removing the tail cone?

July 21st, 2014, 08:45
I've done it numerous times without removing the tail cone. The only really difficult part is getting the new seal in straight. I've replaced a lot of seals and almost do it by feel. Do like 5-90 recommends.

I always jack the rear end up high, so the oil in the transfer flows away from the rear seal end. I honestly can't tell you what will happen if you try to do the job with the XJ flat on the ground (or as flat as they get, most sag in the rear anyway) all the oil may or may not stay in the transfer case, how much is going to flow out when you pull the driveshaft is anybodies guess.

It may be the bushing is worn and this may be the reason the seal is leaking in the first place. Just replacing the seal may not last long. If the shaft has a lot of play in the bushing, the seal is going to wear out quicker.

If it was just a drop or two I'd ignore it. Just periodically check the oil level and keep and eye on how bad the seep is.

I've replaced the bushing without buying a whole new tail piece. It was touch and go for awhile whether the bushing was going to come out or the tail piece was going to explode. I think I was lucky. If/or when I do it again I'm going to buy a new tail piece with the bushing installed.

Matthew Currie
July 21st, 2014, 14:48
I did it a couple of times, and getting the bushing out and back in is helped a good deal if you get a piece of threaded rod and the correct size washers, tubes, etc. to make a home made puller and installer. You can push the seal in with a similar tool too.

When I did it I just took the tail cone off, and the oil did not come out of the TC. Of course, it had leaked some, and now I don't remember how much I added after the job was done. I would not worry much, though. Put a pan under it and take it off.