Can I rebuild this np231?

Hey all - long story short, bought my first XJ earlier this week, 95 AX15 on a 6.5" lift with 35s, otherwise mostly stock. Sounded a little noisy when I test-drove it but I didn't know any better.

Going down the highway on Thursday and the rear driveshaft u-joint let go - very dramatic. Had to beat on the driveshaft for 20 minutes to get it out of the transfer case when it should have slipped right out.

Here's what the output shaft looks like now:



Look how off-center the output shaft is - no wonder it was so hard to get out. Also, note that NO FLUID ran out - which means she was dry.

I went looking for another np231, but it's so confusing which np231s will actually work, and it's very possible only one from a 94 or 95 manual would work. And, it would be worn anyway - so I'd like to rebuild mine if I can, but I've never done it.

My concern is that I'm not seeing a new output shaft in any of the rebuild kits, and it's hard to believe that mine could not be screwed up. Am I wrong on that? Or are they somehow bulletproof and everything else in there is screwed up instead? If it makes a difference, I'd also like to install an SYE (since there wasn't one on a 6.5" lift - no wonder the u-joints gave it up!!) - any chance that would change things for me?

Thanks a lot, all - I truly appreciate the help!!

SYE will come with all you need, just also buy a rebuild kit with new chains etc and youll be fine.

Man, thanks for the lightning reply!! That's great to hear; if you don't mind, which kit would replace the output shaft? I'm reading that SYE kits go *over* the existing shaft but I'm not seeing output shafts in the rebuild kits either :/ I gotta be wrong on one of those!

The SYE kit replaces the output shaft with a new design shaft. You will also need a new driveshaft, some outfits can do a package deal on both.

Great to hear. Man, it's a relief to hear I can rebuild this since it's so hard to find an np231 out of a 94 or 95 manual!! And I'll know it's strong. Thanks all!

While an SYE kit and new driveshaft will probably cure the problem, I would disassemble the transfer case first to see if any other damage occurred and what parts are needed to bring it back into operating condition.
It's a good time to upgrade to the wider chain and sprockets to handle the stress of the 35"s.

That^^^^, plus depending on your intended use also consider a 2 Low kit! A 6 gear planetary is also a HD upgrade.

Ok, good things to think about now - this is on a 95xj ax15 with 35s, 6.5" lift, about to order an SYE. Will have 8.8 4.88 rear with Detroit locker, d30 4.88 front. I'm brand new to the xj game and have only done light wheeling in my Silverado previously - how much do I need to build this thing? There are a lot of other places I need to spend money so I want to do it right and be done but don't want to build it any tougher than I have to. Not planning to abuse it really - will have some fun wheeling but not planning to beat her up.

Thanks all!

That depends on who is doing all the hard work(gears/welding).

So both front and rear already have the gears in them, and the 8.8 is coming out of an xj - so I'm hoping there won't be either one!

Thetastycat said:

Ok, good things to think about now - this is on a 95xj ax15 with 35s, 6.5" lift, about to order an SYE. Will have 8.8 4.88 rear with Detroit locker, d30 4.88 front.
- how much do I need to build this thing? There are a lot of other places I need to spend money so I want to do it right and be done but don't want to build it any tougher than I have to. Not planning to abuse it really - will have some fun wheeling but not planning to beat her up.

Click to expand...

A rig at 6.5", on 35"s ? You have gone big and it will need a lot to make it a reliable and fun to drive off-roader.
A few as follow. Frame reinforcement, Skid plates, Recovery points, Better front and rear brakes, Alloy front axles, Upgraded cooling (radiator and additional coolers), Upgraded steering linkage, More powerful steering box and pump, More power to pull the big tires, the list goes on and on. It isn't going to be cheap.
You will never be done with it, there is always something that needs upgrading, repaired or adjusted.

For more casual use, a shorter rig on smaller tires maybe a lot more useful and will be a lot less work and money to make it reliable and to maintain.

I'm going to be honest, I didn't want to read that, lazy - I figured I've got a few major things in front of me and then I can start to use and enjoy her. But the more I thought about it, the more I realized you are right - XJs weren't intended to be on 6.5" and 35s from the factory, so a lot of them weren't built to handle those well.

But

I want a rig on 35s at 6.5". This is not a daily driver, but a toy, and I have all the time in the world to mess around with it and do stuff like bigger brakes, steering, frame stiffeners, etc. Will it be more work than a modest lift and smaller tires? Yes. But do I want it? Yes. I'm willing to put in the work - it's actually part of the fun for me!

Respect!


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Thanks, brother - I'm about to update this thread with some pics and all the things I've done to her. I took this thread at face value and started upgrading - way back in May! It's been a wild ride (and never will be done) but I've done a ton to her and really had fun along the way.

Will update soon!

Rebuilding the transfer case is not that bad at all. Just make sure you have a good set of snap ring pliers. Bearing pullers would be helpful too especially since it has been run dry. I ran a similar setup (8" lift with 35s and 4.88 gears) for a decade and did not up grade the transfer case beyond a SYE and I never had any problems with it.

Frame stiffeners run around $300 and if you have a welder you can do it in a weekend yourself. $500 spent now on a welder will pay for itself the first time you use it and welding is fun and interesting. I put some on my XJ and it makes a world of difference. It will also increase the lifespan of your jeep dramatically. Once the unit body starts to crack and bend the problems that come with that can get really bad and very difficult to fix. If you are gonna keep that jeep for a while and plan on flogging it off road I would highly recommend a frame stiffening kit.