Anyone experienced with the NP231 - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 05-01-2000, 11:18 PM
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Anyone experienced with the NP231

I bent me main output shaft on the NP231 transfer case on my 91 YJ. I tracked down a scrapped one. Wondering how hard it is to swap the main shaft over, Ive already removed the transfer case but not sure if it is a job to do myself or should I bring it to a professional transmission shop. I know this shaft gets changed when a slip yoke eliminator kit is installed so maybe it's possible for me to do it myself. Any help would be appreciated, I know this is the perfect time to install a slip yoke eliminator kit but I don't have the time. My Jeep is still my daily driver and I need it by next week.
Thanks

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post #2 of (permalink) Old 05-01-2000, 11:54 PM
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Re: Anyone experienced with the NP231

I did it when i did my SYE. if you have a clymers/chiltons manual, it should have a Schematic(sp) inside. it took All day, under the jeep. could do it in under 4hrs now, and on a bench. It wasn't all that hard really... One piece of advice is to unbolt the front D/Shaft yoke B4 you try to take off the Chain. And buy new c-clips before you need them.
Good luck
BJ

"If you chose not to decide, you still have made a Choice" RUSH
post #3 of (permalink) Old 05-02-2000, 10:54 AM
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Re: Anyone experienced with the NP231

I think there are different kinds of 231s, but if yours is like mine, you should have no problems as long as the bending didn't hash anything inside. Did the output bearing in the tail cone get messed up at all? Since you have it out of the Jeep, it should be much easier, and healthier for the back to work on. In anycase, the 231 seemed faily simple to me, so you should be able to save alot if you repair it yourself. Like was already stated, the *first* thing you're going to want to do is take off the front driveshaft yoke. I'll describe the rest of the process on a 231 from a TJ since I just ripped it apart two days ago and its fresh on my mind. The next part was the hardest for me. You need to get an oil slinger off the old shaft. Its a simple piece of metal thats pressed onto the shaft. A gear puller might work, mine didn't and I had to destroy it to remove it. Next take out the retaining ring that is holding on the oil seal. Unless you have retaining ring plyers, this job will be very annoying so try to get some. Take out the oil seal. Take out the next retaining ring (the one on the shaft, not the big snap ring one that holds in the output bearing) Take out the speedo thing if you haven't already. Unbolt the tailcone housing and take it off. That bizzare flat peice of metal that is kinda loose on the shaft is the oil pump, just leave it there for now. Now unbolt the bolts that hold the two case halves together. You might need a 10mm *12-point* socket for one of the bolts, mine had one for some dumb ass reason. Set the case so the tranny mount side is on the bench and pry the case apart using the screw driver notches so you don't mess up the mating surface and cause a leak later. The oil pump should come out with the rear half. Be careful of the round magnet that is right below (installed orientation) the front output shaft, but it shouldn't fall out if the case is on its end. Take off that little spring on the shift rod. Now take a hold of the front and rear output shafts (one in each hand) and pull them both out, the chain will come with them. If the shifter fork tries to come out, don't let them. On the rear shaft, there are two sprocket thing that are slid on from the front and held in with a bgi retaining ring. Take that ring off, pull the bent shaft out and put your new one in and reinstall the snap ring. Now just put it all back together in reverse. (housing bolts 30lb-ft, tailcone bolts 20lb-ft, yoke 120lb-ft) When putting the two halves back together, make sure that the oilpump, and its little attached screen are on like they were before. (the little tabs on the oil pump *must* be on the outside of the big hole in the rear half). Then when putting the rear tail housing back on, make sure those tabs mate up with the little slots that are machined for them in the mating surface of the tail cone. Good Luck man! Be sure to check the output bearing in the tailcone one you get it off. I dont' know if those thing can be hurt, but the bending of the shaft had to cause quite a load and its better to be sure. It your tail housing or that bearing are wrecked, I have the one I just took off sitting around waiting for a new home.
Mike

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