NP231 Rebuild Problems -
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post #1 of 6 Old 06-06-2021, 08:34 AM Thread Starter
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NP231 Rebuild Problems

1996 Jeep Cherokee XJ Sport
4.0L, auto, NP231

First forum and first post - I hope I’m doing it correctly.

In the process of rebuilding transfer case but have couple problems.

1) my range shift fork and hub were toast and need replacement. Problem - the old part has casting number 16976. When I search for a new part (every online source possible or so it seems) I only find a new part with casting number 17833. I can only find used parts with original casting number. So, I bought one of each, a used 16976 and new 17833. They are similar but have enough differences to question the new part is a replacement for the old part. I’ve done lots of searching on internet and the ambiguity is maddening. IS 17833 A TRUE REPLACEMENT FOR 16976 on my 96 XJ with NP231?

2) I think that I trashed the used replacement 16976 that I ordered by trying to replace the plastic pads. I ripped out the old “molded in” pads before thinking things through and none of the new pads fit. The “molded in” pads are nothing like the design of the new pads. The casting uses holes with pegs rather then clip on with slots for positioning. Thoughts?

3) I ordered a used replacement range fork hub in great condition trying to save money. It is different than the original and question if new (used) is valid replacement for the original. Original hub has continuous internal splines. The used replacement has two gaps in the internal splines (three spline segments). At first glance it seems like it will work fine but I don’t fully understand how everything works together in order to have high confidence in my decision to use it. Should I be concerned?

4) after new bearings and seals, when reinstalling planetary gear set I noticed something questionable. After pressing the planetary gear into the input bearing it rotated with minor resistance. However, once I installed and tightened bolts on the bearing retainer the gear set rotated with much more resistance. It is smooth but takes more effort to rotate. Is this normal?

Any help is appreciated.


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post #2 of 6 Old 06-07-2021, 02:33 PM Thread Starter
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Follow up to problem 4) I am comparing the original assembly with old seal to reassembly with new seal. Will a new seal add noticeable resistance on input gear shaft?
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post #3 of 6 Old 06-10-2021, 07:46 AM Thread Starter
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Did I post this incorrectly?
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post #4 of 6 Old 06-10-2021, 01:19 PM
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1993 YJ Wrangler 
Join Date: Jan 2005
Location: Albuquerque
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Originally Posted by TDENXJ View Post
Did I post this incorrectly?
No, you posted fine. Since there are 418 views of this post so far, I suspect no one has run into your problem with enough recollection to give good advice. The last time I rebuilt my NP231 was in 2005. I opened it again in 2012 to add a new chain. I honestly don't remember things to the detail you need. This is generally helpful sub-forum, so hopefully someone can help.

'93 YJ, '02 GM 4.3V6, SOA, dual ARB's, 8.8+D30(WarnHubs), 4.88s, 35" Patagonia M/Ts, AX15, NP231+4:1+SYE+2LO, York OBA.
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post #5 of 6 Old 06-11-2021, 09:03 AM Thread Starter
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Thank you for your input JeeperDon.
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post #6 of 6 Old 06-21-2021, 12:01 AM Thread Starter
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After talking to tech support from various sources like Novak I decided to move forward with the 17833 range fork and the used range hub. Rebuild and reassembly with AA SYE went well until the final bench test. I can only shift between two range (mode?) selections. I shifted into 4low before I removed t case to begin with and thought that I was mindful to reinstall in 4low. I checked the shift rod (in what I assumed was 4low) and it was just under 1” length through the case. I was mindful to check direction of mode hub but could have been distracted by kiddos. Of the two available range (or mode?) selections available - 1) input and two outputs move together. 2) input and rear output move together but I can grab and stop the front output from moving. In what I thought was 4low, the lever points downward but not straight down (perpendicular). It’s angled forward about 25deg. In this lever position, input and both outputs move together and I can see the shift rod max out (just before touching the threads for the brass plug on AA housing maxing out the available space in that blind hole. As this was my first attempt at this I can only assume I made an assembly mistake somewhere. Before I break it all down again and clean off the RTV (hate this part) are there any thoughts or suggestions?
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