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Np231 transfer case questions

2K views 17 replies 7 participants last post by  MuloChico 
#1 ·
This will be a bit long, but I need to explain.

I'm knowledgeable but fairly inexperienced with Wranglers. My son bought a 1988 with the 4.2 about a year and a half ago. Seemed in fairly good shape and we have been pretty happy with it. It's needed some care and attention, but overall a good deal. A few weeks ago he told me it was making some odd drive line noises and we decided to park it until I could look at it better.

A couple of days ago I got under it and found the rear output shaft seal had slid out onto the slip yoke. I checked the fluid and it was dry (had checked it 2 months ago and it was still topped off after replacement 1 1/2 years ago, no leaks).

I bought a seal and some fluid (1st step), replaced the seal, added the fluid and ran it in the air. Fluid came out the rear seal and the shaft was loose (I knew it was a little when I checked the seal, but I didn't think it was that bad). I figure the bearing is shot. I also noticed the pinion angles are off between transfer case and rear end.

Now the questions:
1) Is the transfer case shot, or rebuild-able, or just the bearing for the output shaft? (I'm leaning toward rebuild but I will be pulling it to find out more probably after the 1st of the year. No outward damage to case)
2) Now would be a good time for a SYE/Driveshaft replacement, I've seen the videos and it doesn't look that hard. What about cost details on what is needed?
3) The previous owner put a lift on it but had put the wedges for the pinion in backwards (angled to far forward) so that should be an easy fix.

Any input will be appreciated. I will be taking it all in and making the best overall decisions ($, time, etc) with my son to make this right. We want it done to last as he wants to keep it for a long time to come. I always buy used, so I am used to fixing others shortcuts. I just wish we had seen the pinion problem sooner.

Thanks to all ahead of time
 
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#4 ·
A picture of the drive line from pinion to t case wouldn't hurt but it sounds like angles were off causing your dilemma. Loose drive line could be some internal damage requiring more than a rebuild. Being lifted more than 2-3" an SYE and drive shaft would be a good idea. T cases with SYE's are sold used quiet often. Sgt Jeep a little bit south of you could help you. Or you can just go new with Adams drivehaft or Tom Woods. Just some options.
 
#5 ·
Should be able to be rebuilt assuming the case itself isn't trashed inside.

Now is the prime opportunity to put a SYE in. You will need a new driveshaft and to set the rear pinion properly.
 
#13 ·
JB Conversions has the best SYE on the market in my opinion. Advanced Adapters makes a very good unit and all the others are basically clones of theirs.

FWIW, you can pull a front driveshaft out of a Cherokee and have it cut down to fit with the SYE cheaper than having a whole new shaft built. Assuming cost is a concern.
 
#11 ·
Thanks, that lines up with what I'm finding online. I appreciate all the input. We plan on pulling the transfer case in a few weeks (Schedules, holidays, getting counter space in the garage), then we will have a better idea just what we are in for. I'm just gathering information so I have a better idea of options when we get the case apart.

It also has about a 1" transfer case drop that I plan on removing when we do the SYE/Double Cardan as I have read that the lift isn't a problem with that setup. As best as we can figure it only has about a 2-3" lift. He wants it higher eventually, but for now, it works.
 
#12 ·
From the pic, the pinion angle is terrible at the diff. It should not angle up like it does.

The rear housing has a bronze or brass bushing rather than a bearing for the driveshaft slip yoke to ride in. It is not very difficult to replace.

I agree that a SYE is the best option and get rid of the t-case drop...... but..... you speak of possibly increasing the lift height further down the road. A SYE driveshaft is not cheap and after you lift the vehicle later on you may possibly need to change the driveshaft length again, thus purchase another drive shaft. I would carefully think ahead for future plans vs. today to prevent myself from buying two driveshafts in the end.

Judging by your pics right now the rear axle shims are doing harm, not good.
 
#14 ·
From the pic, the pinion angle is terrible at the diff. It should not angle up like it does.

The rear housing has a bronze or brass bushing rather than a bearing for the driveshaft slip yoke to ride in. It is not very difficult to replace.

I agree that a SYE is the best option and get rid of the t-case drop...... but..... you speak of possibly increasing the lift height further down the road. A SYE driveshaft is not cheap and after you lift the vehicle later on you may possibly need to change the driveshaft length again, thus purchase another drive shaft. I would carefully think ahead for future plans vs. today to prevent myself from buying two driveshafts in the end.

Judging by your pics right now the rear axle shims are doing harm, not good.
Thanks for the info on the bushing, that is a different beast than a bearing. I have a FSM on PDF. I will be looking into that in a couple of days.

My son has ideas rather than plans for a higher lift in the future. Probably at least 5 or more years in the future if he does it at all, but thanks for reminding us to look into the future. Yes, I do agree that the shims are doing more harm (no good). Once we get the plan together for the transfer case we will figure out the best plan for pinion angle.

JB Conversions has the best SYE on the market in my opinion. Advanced Adapters makes a very good unit and all the others are basically clones of theirs.

FWIW, you can pull a front driveshaft out of a Cherokee and have it cut down to fit with the SYE cheaper than having a whole new shaft built. Assuming cost is a concern.
I had not seen the JB Conversions SYE. I've seen some packages with the Advanced Adapters SYE and several different possible driveshafts. I'll look into them.

Thanks for the ideas/options. This is what I figured I would get for this forum. We do appreciate it. :grin2:
 
#17 ·
fishadventure, thanks for the ideas. I almost was going to forget to look at the front driveshaft, after seeing the less than quality work on the rear I need to look the Jeep over better. The idea for the XJ shaft is worth looking into. I've had a local shop recommended by a guy I work with, but I will check with those you mentioned also.
 
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