Np231 Rebuild And Upgrade

[skidoo_j]

I recently took on the project of rebuilding an NP231 from a 97 xj sport to install into my Comanche.

 

 

Biggest lessons I've learned:

 

DO NOT PULL BEARINGS until you have the new ones in hand.   Oh you ordered a master rebuild kit, it came with 6 bearings.   Oh wait the fing kit doesn't come with the correct bearings.    

 

 

Don't remove seals until you have their replacements in hand, yet again the "kit" didnt include the seals needed.   But it did have 5 seals that fit ????    

 

Be careful when removing the snap rings because yet again the kits don't come with new ones.   Get the correct tool!  

 

In 97 they apparently changed the input pilot bearing (the one that goes into the input gear that the main shaft rides on) to that of the 242.   It's more of a cup style.   The bearing is marked torrington DB-59856 and based on my research is timken FC66561   or jeep 83503507.    The problem is nobody has the bearing, and nobody knows when they'll get one in except the dealership who wants $86 plus freight.   

 

 

So out of this $125 rebuild kit I've used 2 bearings and 2 seals.  I'm pretty sure I've got enough bearings and seals for someone else to rebuild an older transfer case.   

 

 

 

Now that the rant is over I will post pictures of the tear down and modification of a $15 tool from autozone to pull the bearing in the rear cover for the front shaft.   It maybe a few days as I'm going to probably have to wait an additional week for the correct parts.  

[Bounty Hunter]

Cool, looking forward to the pics of this tool.

 

I rebuild and upgrade a lot of 231's for folks so post up if you have any questions.  What upgrades do you have planned?

[skidoo_j]

Well the Transfer case is about 90% reassembled.  Just waiting on the re - re- reshipment of the install kit hoping this time it comes with the inner input bearing for the correct year.     

 

 

My Upgrades: 

1.25" Chain

6 planetary 

Terra 2 low

Novak Cable Shift Linkage

Advance Adapter HD SYE

Tom Woods Non-cv shaft (I think my angles with the extra 4" are fine as I didnt want to turn the axle with shims.  And I didnt want to cut and turn)    THis will also allow me to in the event of sale pull and reinstall stock stuff back and sell to recoupe.  

 

 

 

Resources:  

NP 231 Tear down for input shaft change

NP 231 Component service manual (pm if you want a copy)

Advance Adapters Install Manual

HD upgrade     Sourcing your own 6 planet  Building your own 6 planet

Stus offroad

 

If you decide to do the 6 planetary it is year dependent as they changed the cut of the gear for the input. If you do what I did and get a donor transfercase you have to get the correct spline input and gear cut.   I found that you literately have to pull your transfercase to see what you have as our trucks seemed to always be in a transition year.  Options were 21 or 23 spline  and each has long short or medium.    Novak has decent information regarding this   here's a forum that goes over comparison and shows different appearances of the cuts and lengths.  then difference between 231 and 242

 

 

Specialties Tools to buy cheaply from harbor freight or borrow from autozone or other loaner tool programs

 

Bearing and Race Driver set

Slide hammer

Pilot bearing puller from autozone (modified to pull the bearing in the rear case half for front output.  as no blind pullers would work on 1.5" and cheapest blind puller i could find was $100.   )

 

don't go too cheap on these:

lock ring pliers   (these are not snap ring pliers i used lisle 44900)

snap ring pliers

[Bounty Hunter]

How were you able to use a non-CV shaft with the SYE?  Simply running a different fixed yoke in the rear?

I also run the wide chain, 6gear planetary, 2lo, and SYE.  Much more strength than my 4banger needs.

[skidoo_j]

I rebuild and upgrade a lot of 231's for folks so post up if you have any questions.  What upgrades do you have planned?

Does that mean you maybe interested in Buying the remaining extra parts?   PM if so.

How were you able to use a non-CV shaft with the SYE?  Simply running a different fixed yoke in the rear?

 

I also run the wide chain, 6gear planetary, 2lo, and SYE.  Much more strength than my 4banger needs.

If you run a double cardon drive line you have to rotate the pinion to driveshaft to 0 degrees.   As long as you keep the pinion parallel to the transfer case you can run fixed yoke with a slip shaft.   So my slip is in the shaft just like a "cv" however I only have two u-joints instead of 3.   And yes there is a different yoke, a U-bolt style, Tom Woods swapped it prior to shipping at no up charge. 

 

My driveline angle is about 13*,  I get very few vibrations since I got a 3/4" longer slip yoke for more spline engagement.  So i figure with the fixed yoke my overall driveline will be about 4" longer and bring my angle to about 8*.   Ideally you want 3*  so i'll get about 50% life out of my ujoint, but the angle should not be significant enough to cause vibe (so i hope)

[skidoo_j]

Got it installed in the truck tonight.   Test drive is tomorrow.   I may wait awhile before i hook up the electric switch to the dash.  Probably when I remove the posi disconnect and do a single axle swap.  

[skidoo_j]

Because this is so well documented on other forums I'm only posting a handful of photos.  Step by step and more can be referenced in my links I posted earlier for information:
 
 
Output shaft of 89 ax15 23 spline: 

Input shaft of NP231 from 89 comanche 23 spline short: 


 
Comparison for HD vs Stock




 
3 vs 6 planetary 



 
The front output rear bearing that's a PITA to remove and my modified autozone tool 27059.  modify by grinding the teeth to 1/16th,  take a bolt and grind two sides so it will fit inside so you press the arms further apart to catch the inner bearing lip.
 

 



Novak Shift cable 

 
Complteted 97 transfer case w/ AA sye this is a medium length 23 spline input shaft