NP231 rebuild

RenegadeT

RenegadeT

no shirt,no shoes,no dice
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Mar 24, 2005
Location
Stokesdale-Greensboro
It looks like I'll be pulling the 231 from my DD 99 XJ, its making a bad growling noise, sounds like from the front output side. Under deceleration, it sounds like a jake brake coming on. At first I was thinking front axle, but the noise seems more like the t-case area, maybe the chain. 4HI seems to be working, I didnt check 4LO. Recently, it started bucking, jerking the entire vehicle, so I pulled the front driveshaft. That eliminated the bucking (on my one test drive, it could come back I suppose), but the growling is still there. Rotating the front output yoke by hand didn't sound or feel too good either.
I suppose I should've checked the fluid. Its got 163k miles on it, I am the only owner and I know that the only lube in there is what the factory filled with in 1999.
Any ideas on what might be going on? What parts should I be prepared to replace if I pull/split the t-case?
 
My friend had the same problem with his 231. It didn't get to the bucking and jerking stage, but it made a loud noise on deceleration. It turned out to be the chain. My father in law's dakota had a 231 in it and it would pop and jerk in 4wd and it turned out to be the chain. I would replace the chain and bearings while your in there. I would also look over the pads on the shift fork. There not expensive but sometimes difficult to find. Might as well do it right if your going to all the trouble to drop and fix it. The parts aren't all that expensive. I think the last one we did the chain and bearing kit with seals was around 180 bucks for all the parts.
 
Tony it sounds like the shift fork isn't locking into the detents like it should. Try driving around and getting it to make the noise. While the grinding is happening move the shifter around. If the noise changes or goes away you'll need to pull the back half of the case off and see whats going on. My guess would be that the rear output bearing is bad allowing the main shaft to move fore and aft. That'll let the shift collar grind on the teeth for the front output. The other thing could be that the plastic like isolators on the tips of of the fingers on the shift fork are badly worn or missing. Causing the shift collar to slop around.
 
well, I finally dropped the t-case and pulled it apart, everything looks right...but I have to admit I don't really know what I'm looking at.

Before I pulled the front yoke to remove the chain, I could duplicate the grinding noise by pulling the mainshaft away from the front output...simulating a looser chain. I convinced myself the chain was the culprit.
So I pulled the chain, it "looked" OK, felt a lil loose, but I dunno.

Looking closer, I think Chris MarsFab might be onto something. The noise seems to be the synchro? gear on the mainshaft rubbing the backside of the shift collar (thing with the white mark in pic I'll try to attach). I'm not sure if a tighter chain will fix this or not. Its like mainshaft needs to be held rearward a bit more, or the shift fork needs to move forward somehow. Shift fork pads look great too.

Try a new chain and see what happens?
 
IMG_20130905_192948_172.jpg
 
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