PAGE 1 Intro
PAGE 2 Tires, Wheels, Suspension, and Steering
PAGE 3 Audio
PAGE 4 Exterior Modifications
PAGE 5 Interior Modifications
PAGE 6 Under-the-Hood & Engine Modifications
PAGE 7 First Accident
PAGE 8 Second Accident
PAGE 9 Dirty Pictures
PAGE 10 NP249 to NP231 Transfer Case Swap (You Are Here)
PAGE 11 4X4 Show 2007

NP249 to NP231 Transfer Case Swap

OK -- this project from hell is finally over. Here's an overview of the install for those interested in doing it themselves. If you have any questions about anything, don't hesitate to ask -- I'll more than likely be able to answer them. This walkthrough may not be totally complete because many times I didn't have time to stop what I was doing to take pictures -- I just wanted to get it done. So, if I missed anything, or if there is a step you're not sure about, just ask.

First things first. Take the stress off the rear driveshaft by pulling the ZJ up in the driveway a few inches, then chock the wheels. This is a very important step -- it will save you a lot of grief -- trust me. If you want to hear my horror story, ask me; but I'm not gonna post it on here.

Now is a perfect time to start draining the NP249. The NP231 should be drained and ready to put new fluid in (1 qt. Dexron III ATF).

First, remove the shifter handle, shifter bezel, and center console. There is a plate that pops out under the emergency brake which makes this very easy.

Then, undo the 4x4 shift plate by removing the four screws. This allows the plate to come out once the linkage is undone.

This is the shift bracket that needs to be unbolted and removed.

This is what is known as the "Z-gate." It is all of the shift linkage that needs to be removed. Start by pulling the rod that is connected to the shifter handle out of the rubber bushing (shown in pic on the right). After this is done, the whole shifter assembly comes right out of the floor.

Remove the rest of the shift linkage by unbolting it from the Z-gate block and pulling it out of the rubber bushings.

Next, mark the position of the driveshaft on the rear diff. This is VERY IMPORTANT!

Sorry about the poor quality, but this pic shows the straps and bolts taken out of the yoke in the rear diff. MAKE SURE YOUR WHEELS ARE CHOCKED!!! GOT IT?! Take a heavy hammer and lightly tap the u-joint out of the yoke. Remove the driveshaft from the transfer case. Some ATF may leak from the slip yoke, so watch your eyes!

Now here comes the fun part. Time to unbolt the NP249. Sounds easy, right? Well, it is, for the first 5 nuts. The top nut is a complete BITCH to get off unless you have a very special tool... all I need to say is: Make sure you have a sacrificial 9/16" box-end wrench. Undo all the nuts with a 9/16" box-end. They all come off, but it may be tough -- just put some elbow grease into it (and make sure you have thick gloves on -- I didn't, and now I've got a nice scar on the back of my hand right over a major vein -- that could've sucked a big one).

Now for that special tool: Take a spare 9/16" box-end and cut it in half using a bench grinder. Then, use the grinder to put a notch in the top of the wrench. Okay, now put the box end over that top nut. Take a long, thin nylon rope and put it over the notch. Then, get a couple friends to help you. This just goes to show you how much of a bitch this nut is -- it took 3 of us to get it undone. Make sure the rope is wrapped under the transfer case (just think of your high school physics class and what you learned about leverage). Then do this...

Jordan, me, and Adam. Thanks, guys!

Now time to take the NP249 out. Make sure you have a drain pan ready -- it could get messy. Push up on the t-case and ease it away from the transmission. Mine got stuck on the underbody of my Jeep, so we wrapped the rope around the t-case and out the rear of the Jeep, and had Jordan (the big dude) yank on it a few times to dent the underbody just enough to clear the t-case.

Lower the NP249 down carefully (make sure you can bench press at least 80 lbs). Try to shift it from your chest to a creeper, so it is easier to get out from under the Jeep.

Here's the part that sucks because it's really a hit-or-miss chance. Count the number of splines on the input gear of both t-cases and make sure they match up. If they don't, that sucks, but there is still hope. You will have to take the t-case apart and take the input gear assembly out and swap them. For some stupid reason, Jeep decided to change the cut of the t-case input gear around 1995, so you'll know if they do or don't match up. Now, keep in mind, they will both fit in and seem to work until you actually turn the input gear -- it will make a rough humming sound if you spin it fast enough. If it doesn't do that, then you're all good, and can continue.

Case halves apart.

Unbolt and pry up on input gear faceplate. Make sure you have a good set of snap ring pliers to take that ring off.

Input gear assembly out of my NP231.

Input gear assembly out of my NP249.

If it doesn't match up, you will need to purchase a new input gear. They run about $160 shipped. Go to www.novak-adapt.com to find the chart of input gears to determine which one you need. Once you get it, swap it into the planetary housing, and put it into your NP231.

I went ahead and installed a new oil pump ($60) while I had the thing apart.

New input gear installed in NP231.

Make sure EVERY surface that was taken apart and had sealant on it is thoroughly cleaned of all old silicone and is resealed. Be sure to use the black stuff for everything.

Installation of the NP231 is the reverse of removal of the NP249.

Fill the NP231 with 1 qt. of Dexron III ATF. Also be sure to fill the tranny up with some fluid to compensate for whatever was lost during the swap.

Install the shift linkage from Novak according to the instructions supplied.

I had to put 1" transfer case drop bushings between my crossmember and underbody because I had too much lift to keep my driveshaft at low enough angle as to where it would drive with no vibrations.

And here is the solution to from keeping mud, and whatever else Mother Nature wants to put in your Jeep, out: First, I cut a sheet of rubber and screwed it to the under side of the ZJ (barrier #1, not shown). I bought a rubber shift boot and placed it over the new shifter and screwed it into the floor board (barrier #2). And to cover up all the ugliness, I went ahead and bought another shift boot (this one is suede) to make it look nice.

Good luck with your swap, and like I said, if you have any questions, go ahead and ask them -- I'll answer them for you.

Also, if anyone is interested in buying spare NP249 parts, email me at keeperofthecage54@comcast.net.

Now go out and have some fun!!!

*****March 21, 2007 -- Pulled my transfer case out and did a Master rebuild kit on it. All new seals, bearings, and o-rings, etc. Also upgraded to a wide chain kit (new wide chain and wider drive sprockets); both purchased from JB Conversions. The good ol' NP231 is a lot stronger now!! Sorry, no pics*****

PAGE 1 Intro
PAGE 2 Tires, Wheels, Suspension, and Steering
PAGE 3 Audio
PAGE 4 Exterior Modifications
PAGE 5 Interior Modifications
PAGE 6 Under-the-Hood & Engine Modifications
PAGE 7 First Accident
PAGE 8 Second Accident
PAGE 9 Dirty Pictures
PAGE 10 NP249 to NP231 Transfer Case Swap (You Are Here)