I think my NP231 is dying (video)

Yoda

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Ouch. So I posted a month or so ago about what I thought was chain noise in my NP231. When I took right turns I'd get a slight rubbing/grinding sound, kind of like something spinning was rubbing against something that wasn't. It was very subtle and only happened when accelerating on highway on ramps. Front driveshaft is fine, no signs of wear. Can feel the vibration in the 4WD shifter handle. Now the bad part....

Over the next few weeks the sound got louder and louder and started to do it all the time. Sometimes I could lay off the gas or hit a bump and it would go away for a while. Thought it might be the linkage or a loose chain I thought I would just remove the linkage first and keep it in 2WD just to rule some things out. Still makes the noise!!! And FYI the linkage was sloppy so I'm not sure I was 100% engaged or disengaged. I can use a pry bar and cycle through the transfer case gear positions just fine. It feels normal when I shift it manually.

Now it is howling! If I hit a bump the right way or get underneath and play with the shifter arm the noise might go away a bit...but hit another bump and it comes right back.

I'm thinking I either have a very stretched chain, or the shift fork is bent and not shifting 100%. Either way I'm heading to the junkyard tomorrow to pick up a used NP231 to swap in over the weekend. BTW, the noise increases with vehicle speed not engine speed.

Here is a video with audio to give you guys an idea. Yes, its a KJ Liberty but the NP231 is the same and you guys tend to be the most knowledgeable with this stuff so I'm hoping you can help. Thanks!

FYI...the video sounds like it has too much bass. It is definitely not as deep sounding in person. The video starts with me at a full stop and I start accelerating.

 
Changing with speed indicates something in the driveline. It could be a bad ujoint in the rear driveshaft. Its obviously hard for us to tell, but it does sound similar to a sound I had in my rear driveshaft that increased with speed.
 
Hmmmm. I'll check the u-joint tonight, easy enough. When I was under there a few days ago I gave the driveshaft a good wiggle and nothing felt weird. I'll pry on the u-joints and see if there is any play. I'll post back in a bit.

Just one bit more of maybe useless information. When the linkage was connected and sloppy, I could push down on the transfer case handle and change the tone of the noise a bit which is why I'm thinking transfer case.

It sounds like the noise is coming from the transfer case / trans shifter area. Right on top of the input to the transfer case.
 
Driveshaft u-joints are good. No play at all. Because the noise is coming from the area where the t-case and trans meet I'm leaning towards t-case, especially because I can change the tune when I move the t-case shifter. It could be on the output side of the transmission but I'm hoping that's not it.

I checked the fluids, both are full and look good. No burnt sludge.
 
Pull the transfer case, crack it open and take a look...not hard or scary to do... especially if you have a cable shifter.

A new chain isn't hard to install and if you don't have a SYE now's the time.

Another option is replacement...I see 231s all over the place for less that $500 and often just a couple hundred.

You also could go nuclear and throw an Atlas, or IMHO preferably a midnight metalworks D300...doing front digs is awesome.

-Mac
 
A junkyard close by has an NP231 with 70k miles for $175. I'm going to pick it up and swap it in this weekend. The one in there now can be my spare and I'll fix it up.

This is my family hauler and commuter so I can't have too much downtime, otherwise yeah I'd take it apart and fix it.
 
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UPDATE!!

I ended up getting a NP242 from the junkyard instead of another NP231. It's a street Jeep and the full-time 4WD will come in handy in the winters in New England. But bad news! I was noise free for a day and it came back. I'm actually leaning towards the front driveshaft now. Most likely the CV joint on the transfer case side. I'm going to take it out tonight and see if the noise stays away.

Fingers crossed that is it and I didn't swap my t-case with another bad one.
 
UPDATE #2:

I feel kind of dumb lol. I took the front driveshaft out and surprise surprise....quiet!!!! So I made a 30 minute job into an all day affair. Well I got some new tools in the process and now have a better transfer case for my type of driving....but moral of the story is...I should have done the easy things first! When you are thinking your transfer case is going to blow...take your driveshafts out one at a time! A lot easier than swapping a t-case!

The real test will be tomorrow when I drive 100 miles round trip for work. If it stays quiet then....I'm considering this a win, and a learning experience!
 
Pull driveshaft first you must.

You fix what isn’t broken, and the Force is weakened.
 
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Final Update:

Stupid won this round. But I had fun and made some upgrades in the process. I put the front driveshaft back in and the noise was gone for a few days and then it came back with a vengeance! My initial thought was that while taking it out I exercised the CV joints quite a bit and got some grease where it hadn't been before. The driveshaft felt a little clunky so I rebuilt it with new CV joints.

After reinstalling it...the noise was still there!!!! I took the driveshaft back out, quiet as a church mouse again and made the long drive to my dad's repair shop. Put the driveshaft back in and put it up on the lift in 4WD and within 30 seconds he yells "FOUND IT".

I could have avoided the whole fiasco if I zip-tied the t-case shifter cable out of the way. It clamp that held it up was toast and the cable would rub on the driveshaft. No real wear on the cable....but that little friction made a hell of a racket!!!

Oh well. I had some fun in my garage, upgraded my t-case to a n NP242 and rebuilt the front driveshaft for about $150 total. Or I could have just spend 50 cents on some zip-ties.