NP 231 J Rebuild and SYE install -

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post #1 of 30 Old 04-07-2009, 10:57 PM Thread Starter
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NP 231 J Rebuild and SYE install

Always read your instructions that come with your product i use a Rouged ridge super short SYE. Some things may vary from product to product.

First thing you need to do is remove your transfer case. If you don't have a impact wrench you may want to remove the nut on the front U joint flange pry to removing from Jeep. Then you need to remove the front yoke. I didn't this by hitting the yoke with a hammer. Don't hit it with everything you have but hit it fairly well.

As you can see I Always please the parts of every step in a baggie and/or can so I know what goes on when and where.

Then remove the 4 bolts holding on the farthest back pat of the case.

Remove the snap ring off the shaft next to the bearing. Then five bolts that hold on the bearing holder. Light tapping usually will break it lose from the case. NEVER pond on or pound a screw driver or chisel. This will scar the parts where they need to seal and leak. They may have prying spots cast in them. You will see small gaps between the half's where you can pry. The two main half's of this case have that.

At this point you can see the oil pump. Look at it a see how it is placed in there. Where the oil line comes out etc.

Now remove the bolts of the two main half's. The are a couple of pry points you can use on this step. I just taped it in a few place all the way around the case and they cam apart. Take your time and pull it a part evenly on both sides so it dose not bind on shafts.

On the bottom of the case close to the drain plug is a magnet. Inspect it look for broken parts and how many filings are on it. Look at inside of case for signs the chain has Ben slapping against it. I Had sever parts and lots filings. Sorry forgot to get a pick of that and could not get a good one of where it slapped the case. But is a few of the bigger parts i found on the magnet.

also inspect your screen on your pick up tube for your oil pump. Mine was shot.

At this point i knew i need more parts and had to rebuild the case. So much for doing a fast install of the SYE. I need to know everything i need to replace so I disassembled the rest of the case. The next step is to remove the front drive shaft and chain. Use a wooden mallet or hold a block of wood on the threaded part of the shaft and tap out. once you tap the shaft out the chain will come off.

Now look at you sprockets and chain for wear. My sprockets looked great but my chain was stiff and showed lots of wear on every other tooth.

Now with a little wiggling around you can Get the rear out put shaft and shifting fork. (this fork shifts the front drive shaft in and out of gear) inspect you shifting fork and pads at this point. My pads where gone and it wore in to my fork badly.

Now remove the snap ring and remove the gear Assembly from the shaft. At this point i saw where the rest of my parts came from.

Now remove the front shifting fork(this shifts you between high and low range) And inspect the pads and fork. Mine looked great.

Last edited by EZAces; 05-11-2010 at 08:16 PM.
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post #2 of 30 Old 04-07-2009, 10:57 PM Thread Starter
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SO i ordered all the parts for the rebuild.
All the parts and the master rebuild kit.

On older NP231 the drive sprocket has needle bearings in side drive them out they will not need to be replaced with SYE (at least for this kit)

Now I took the front half of the case and used a seal puller to pull the seal.

I used a punch to drive the bearing out. Sorry no pic but later picks show me doing the same thing. Then i drove the new bearing in with a socket just smaller than the bearing. Yes a bearing driver would be better but trying to some some alternatives for people limited on tools.

I used a 4x4 block of oak to drive the new seal in.

Then take the four bolts that hold the plate that holds the bearing and seal of the input shaft.



Remove the snap ring and tap out input shaft. drive the bearing out of the case and the seal out of the retaining ring.

Drive new bearing and seal in place. Be sure to scrape all the silicone from both parts and clean throughly. I use alcohol But paint thiner works as well at end to ensure there is no oils so I get a good seal.

To remove the bearing in the planetary use a long punch and remove.

To reinstall the new bearing Used the used output shaft (sorry no pic). now reinstall planetary and input shaft replace the snap ring. clean the area to be silicon-ed with alcohol or paint thiner. put a thin coat of black RV silicone and and bolt to together. Do not put to much silicone on do not want it in the bearing.

Now you can replace the front shifting fork Assembly.

Now install the gear assembly you removed from the rear output shaft to the new one. Forgot the pick but should look like the one that came out except shorter lol.don't forget to replace the snap ring. Now install it in to the case. carefully aliening everything as you go. Do not fore any thing.

At this point in stall the rear shifting fork and shifting ring. This takes a little work to line everything up as you go. Turn the shaft or ring to help line up splines. don't forget the spring.

Now put the new chain and front output shaft back in gently tapping the shaft into place.

Now put the magnet back in place. check the o ring int the oil pump.( I replaced the oil pump for simple fact i just drooped $550 in rebuilding and $40 pump was cheap insurance. ) replace anything that looks like it needs it. Place black RV silicone on one half the case.

When i put the two half's together i put the oil pick tube and pump in place and held them in place i lined everything up. Needed three hands just for that so did not get any picks. It is very in important to make sure oil pick up stays in groves and hooked to pump as you complete this step. After you get them to together examine oil pump and pick up tube and make sure they are still connected and in prober place. tok to specs and turn shafts on case make sure they turn well.

Now clean and silicone the new SYE casting and install with OE blots.

Now all you need to do is install the U joint yokes and install in your jeep.

Hope this helped you out a little.
And please forgive the spelling that is my weak point.

Last edited by EZAces; 05-11-2010 at 08:57 PM.
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post #3 of 30 Old 04-07-2009, 11:01 PM
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Good write up, minus the spelling and grammar...

I've got my t-case in peices on the bench now. As soon as I get my oil pump from Q-tec, which is on backorder :, it'll be good to go.

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post #4 of 30 Old 04-07-2009, 11:24 PM
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Did you replace the rear bearings for the front output shaft? They gave me more trouble than any other part of the rebuild. I'm refering to the bearings at the top of the pic.

Could the bottle of Everclear in your pics have anything to do with the spelling issues?

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post #5 of 30 Old 04-08-2009, 07:03 AM Thread Starter
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Yes I did forgot to put that part in thanks. Gues thats what i get for writing it at 11 pm I used a bearing puller to pull that out and cant find that pic
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post #6 of 30 Old 04-11-2009, 06:55 PM Thread Starter
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post #7 of 30 Old 05-20-2009, 08:35 PM
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hey man great writeup.

I was putting mine it back together and was at the stage in your very last picture of your first post

The ring thing that sits in the shift fork fell out and tumbled onto my workbench

I noticed that the grove it sits in was offcenter

so i am wondering wich way it going back on. is it offset towards the camera, or away from the camera

she's a real grand Rio Grande: 4" RE, 35" pro comp's, trail damage
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post #8 of 30 Old 05-22-2009, 05:18 PM
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she's a real grand Rio Grande: 4" RE, 35" pro comp's, trail damage
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post #9 of 30 Old 05-22-2009, 09:45 PM
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Great pics and info, but God what a painful read. Try spell check next time.

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post #10 of 30 Old 05-22-2009, 09:56 PM
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Nice write up.
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post #11 of 30 Old 01-16-2010, 06:55 PM
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Thanks i needed that
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post #12 of 30 Old 01-16-2010, 08:02 PM
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Originally Posted by 95jy View Post
Thanks i needed that
Did you use it?

As an fyi, I know some people like to pull the t/c and place it on a bench, yada yada, but I kept mine in the jeep, which helped with that front yoke (especially with the massive torquing!!).

Another fyi, due to having 101k miles on the t/c I pre-ordered a chain, fork pads, and oil ring. Everything looked good, but I still replaced those buggers.

EZ, do you have pics of the master rebuild? That would help out a lot.

As another fyi, here are other write-ups:

Jeep NP231 Transfer Case Slip Yoke Eliminator Install - 4Wheel & Off-Road Magazine

Advanced Adapters 231 SYE install

(t/c in jeep)
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post #13 of 30 Old 01-16-2010, 08:24 PM Thread Starter
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I will look at the pics i have and see if i have a pick of the master rebuild kit
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post #14 of 30 Old 03-05-2010, 06:35 AM
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Ace can you check your pictures, they aren't showing up.

1997 TJ with some stuff done to it.
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post #15 of 30 Old 05-05-2010, 06:58 PM
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Ace can you check your pictures, they aren't showing up.
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