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Old February 5th, 2018, 01:26
HunterDude89 HunterDude89 is offline
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Transfer Case Noise

So I just did a full rebuild and SYE install on my NP231 transfer case. I actually got a whole new (used) transfer case and used it for the case mostly. My original one blew up, blowing the case apart.

So I got another NP231J (a 23 spline the same as my original) and used the case, chain, and the steel range shift fork from it. All the bearings and seals were replaced, and I reused my original planetary gears, range and mode gears (on the new SYE shaft), oil pump, and front output shaft.

I took my time rebuilding it to make sure I did it right, but now that I've got it back in the truck and driving I noticed its pretty noisy. I know it is the transfer case because you can hear it even when the transmission and transfer case are both in neutral...

I did notice some differences between the two transfer cases when I took them apart. My donor transfer case had a synchro on the drive sprocket and my original did not. My donor also had a steel range fork and my original had an aluminum one. Lastly, my donor had a longer rod that the shift forks slid onto than my original (I used my original rod and mode shift fork and gear).

The only things that concerned me during the rebuild was using the steel shift fork (I did this because the pads on my original aluminum one were worn out and I didn't have time to order a new one), and that my chain seemed to sit slightly crooked. I didn't think much of it at the time because I thought I remembered and saw it that way when watching rebuild videos and when disassembling the donor case earlier. The main shaft sat in great and everything fit, same with the front output shaft. When the chain was in the chain sat about halfway into the case on the main shaft side, and level with the edge of the case on the front output shaft side. Is this normal? Could it be the cause of my noise? It spun fine once fully assembled on the bench and when in the truck, and it drives great no weird vibrations or binding or clicking. Just a kind of whining noise, or very slight metal rubbing. I just figured everything would line up a little better once I tightened the front output yoke down. And that if all the snap rings and everything fit right once I got the other half of the case on it was just fine (and everything did go back together fine).

The only other issue I had when doing this project was getting my rear driveshaft to fit. It is a CV driveshaft with a slip and at first it wouldn't extend long enough to reach, so I pulled on it and got all the bolts in a few threads and then slowly tightened each one down evenly until it fit perfectly. I just figured it didn't want to extend fully because it is older and hasn't moved much from its old, shorter, position (my original transfer case had a hack and tap SYE on it, as my new one is a full replacement kit).

I'm just hoping that someone has run into a similar problem or has more experience with this and could help me out. I was thinking maybe all the parts need to wear in with each other or maybe I missed something that was right in front of me. Any input is definitely appreciated!
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Old February 5th, 2018, 01:33
HunterDude89 HunterDude89 is offline
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Re: Transfer Case Noise

Also, I haven't driven the truck with the front driveshaft in yet. If that makes a difference at all, I'm just waiting on parts to rebuild it too.
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Old February 5th, 2018, 07:06
RCP Phx RCP Phx is offline
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Re: Transfer Case Noise

What about all the shift fork pads?
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Old February 5th, 2018, 20:05
HunterDude89 HunterDude89 is offline
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Re: Transfer Case Noise

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Originally Posted by RCP Phx View Post
What about all the shift fork pads?
I replaced all of the shift fork pads and they fit properly
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Old February 6th, 2018, 13:39
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Anak Anak is offline
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Re: Transfer Case Noise

If I understand what you have done, I am gathering that you mixed the planetary gears from one case with the sun gear that is in another case. That may be your issue. The planetary gears may not be happy with the sun gear.

There is an early and a late style input gear, with a cut-off around 1994.

Novak has some details here:

https://www.novak-adapt.com/knowledg...g-input-gears/

You can also do some Google searching and find more information on the topic. I am not seeing what model year either case is, but that is my best guess.
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Old February 7th, 2018, 02:17
HunterDude89 HunterDude89 is offline
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Re: Transfer Case Noise

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Originally Posted by Anak View Post
If I understand what you have done, I am gathering that you mixed the planetary gears from one case with the sun gear that is in another case. That may be your issue. The planetary gears may not be happy with the sun gear.

There is an early and a late style input gear, with a cut-off around 1994.

Novak has some details here:

https://www.novak-adapt.com/knowledg...g-input-gears/

You can also do some Google searching and find more information on the topic. I am not seeing what model year either case is, but that is my best guess.
Thanks man, that link is super helpful! My original transfer case was a 23 spline from a 1999 XJ, and the replacement that I got for the shell and other parts was also a 23 spline but 1996 or older because it had a synchro on the drive sprocket.

I did notice that the input gear shaft lengths were different, but I used the full planetary gear out of my original transfer case. After reading the article you linked I see what you mean. The planetary gears might not be happy with the ring gear that is pressed into the case? That might be it since they mention different gear cuts throughout the years, and I did mix those two parts (planetary from my original with the pressed in ring gear from the replacement).

I would like to know if the gear cut is so different that they would still work together though? Because my truck drives completely fine, it just makes the loud whine from the transfer case.
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Old February 7th, 2018, 07:20
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Anak Anak is offline
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Re: Transfer Case Noise

That noise is probably the sound of different gear cuts destroying each other. I would expect that if you continue driving it you will be starting from scratch all over again.

I will also note that my '96 does not have the brass synchros. I am not sure how far back you have to go to find those, but it is earlier than 04/96.
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