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hooped transfer case / np242 swap discussion

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Hey all,
I would seem the gnomes operating my NP129 are about to go on strike. Ive always known this day would come, as they were pretty beat up and disillusioned when I got the car, and since then, theyve been forced to work odd hours with very little pay and no benefits. The writing on the wall has become much clearer lately.
To any unfamiliar with the history of the car, a short summary is here:
To sum up all thats gone wrong with the TC while Ive had it, Ill be brief.
when I first got it running, the vacuum system was a little boogered and it was stuck in false neutral. I hooked enough of it up to operate the actuator, and it worked, but when it was in 2wd and reverse, it produced a discomforting shudder.
The first time I drained the ATF, a bunch of silicone came with it, so I know the VC is some degree of shot.
I locked the front axle disconnect forward so I could shift on the fly, but when I actually tried shifting on the fly, the transfer case took a while to engage, made a horrible grinding sound, then clunked harshly into gear. I stopped the car to shift it after that.
A couple months ago, I was spinning snow donuts in the work parking lot, as one does when you drive an eagle and it snows 8 inches. On the left donuts, the front tire kicked up enough dense packed snow above the transfer case skid plate that it pushed the linkage back into false neutral and it slammed back into 4wd while the engine was revved up from being disconnected from the driveline. In fact it did this 5-6 times as I limped it back to my parking spot. After that, I dropped the skid plate and investigated. The linkage has a good bit of slop in it between the vacuum actuator and the shift arm. I ziptied the shift arm fully and firmly into the 4wd position, and it worked fine for another while.
Fast forward to last weekend, I was cruising lazily along the highway to my friends place, it pops out of gear and back in at 60mph. Thats a scary one. Now when I drive it around, every once in a while itll start a rhythmic driveline clunk for 5-10 seconds then go away.

Ive worked on and inspected the transmission, engine, both driveshafts, and both diffs, so Im pretty confident Ive got a really stretched chain or a few missing sprocket teeth, and since my long term plan was always to swap in a np242, it looks like Ill be hitting up the junkyards this weekend to find me a new transfer case. Ive read everything I can find on both forums, plus the wiki, and Im pretty confident I can pull it off, but when browsing around, I see a decent number of you mention that you have a 242 as well, so I was just wondering if you guys had any tips or little nuggets of wisdom for me. Were you able to swap the stock shift linkage, or did you use a novak shifter, or something else? The novak looks nice, but $180 seems a bit steep if I can avoid it. Also, what particular methods did you use for negating the slip joint problem? I was going to grab the slip joint off whatever jeep I get the tcase from, stick it on the eagle driveshaft, and disable the eagle slipjoint with a piece of pipe, like Ive seen a few others do, but in my research Ive come across a method from the jeep forums called a "hack n tap" slip yoke emliminator, in which you get a $100 kit, cut all but 1.5" of splines off of the output shaft, then drill and tap a hole in the center of the shaft, slide on the new yoke from the kit, and bolt it to the shaft. Then I could use the eagle driveshaft with no (or less) janky mods.
Anyways, thoughts? comments? tips? lighthearted discussion?

Also, as a treat for everybody, Ill do a teardown on the old one eventually and get pics of all the juicy carnage.

This is what I did to put an NP242 in my 1988 Eagle Wagon, with as many pictures as I could scrounge up.

Which NP242?  Mine came from a 1998 Jeep Cherokee XJ.  Not all had NP242's, so good luck finding one.  I wanted that to keep the full time 4WD capability, unlike the NP231 that seems more common. There is a huge amount of confusing information about input splines and input shaft lengths among different.  Here are my findings, but check that your car is the same: 
* The input shaft on my NP129 was 23 splines, I think this is same for all Eagles. Some jeeps use 21 spline shafts, these won't work.
* My NP129 input shaft extended 2-1/4" past the mating surface of the transfer case and transmission.  Jeeps had three different lengths, 2.1" Long, 1.7" Medium, and 1.2" short. Best option would be the "long" but I could only find a "short" one.  I used an extension seal for the tcase input shaft.  See below.
* You want a mechanical speedo gear, or at least a hole in the NP242 where it should be.
 My 1998 NP242 had an electronic sensor but it unplugged and the Eagle speedo went right back in.
Physical mounting:  The NP242 will bolt right up.  You sometimes read about having problems with the speedo cable, because the Jeep NP242 has it clocked differently.  I didn't have any problem.  It was a bit tighter but I didn't need to split the T-case and reclock the tail section.

Input Shaft Seal:  This is where mine got tricky. 
* Since I used a short input shaft, it didn't stick into the transmission as far as the original Eagle NP129 shaft.  No problem physically, even the short shaft has plenty of engagement and will be strong enough.  Maybe if you were running behind a 600 horsepower rock crawler I'd worry about the shaft not having enough engagement, but not a problem in the Eagle and I saw plenty of examples online of guys mixing and matching even with Jeeps.  Seems like the longer shafts came in Jeeps behind automatic transmissions, and the shorter ones behind sticks. 
* Anyway, strength isn't the problem but keeping the fluid in the trans is always nice.  With the shorter shaft it won't hit the stock Eagle seal - the shaft is too short.  I found an extension seal from a company called Teraflex that moves the seal rearward about .75" which is enough to engage on the shorter shaft.  I saw it online a few places, search for "Teraflex 002904400".  I got mine from Summit I think, for less than $40.
* When you install the extension seal, don't drive it all the way to the bottom of the pocket. You only want to drive it as deep as the original seal, which is made to install level with the outer face of the pocket in the trans housing.  Hard to explain, but see the pictures below. It will take some finesse and measuring about 4 times.  I also put a little RTV between the extension seal the the trans, but not sure this was needed.
Speedometer:  I used the stock Eagle speedo cable.  The Eagle housing will bolt right into the NP242 hole, and if everything else is stock you are good to go.

* I replaced my speedo gear to account for a new axle ratio (I went from 2.35 to 3.07) and big mud tires.  Found a calculator online that told me which gear to use, it was dead on when I finally got on the road.  The gears I found on fleabay, apparently they are the same gears used by old Dodge trucks.  There are also two different housings, depending on how many teeth you have in your speedo gear.  I think the stock Eagle housing was black and will hold 22-25 teeth gears.  I needed a different housing to hold a 28 tooth gear, but got it all from the Dodge speedo gear dude on fleabay.
Front Driveshaft:  The stock Eagle front driveshaft worked fine.  The yoke on the Cherokee NP242 is the same style as the NP129.  The NP242 yoke was a hair longer, but there was still plenty of space in the slip yoke.  Since everything in the front is hard mounted, the slip yoke doesn't see much action in an Eagle anyway.

Rear Driveshaft:  I didn't need to hack n' tap or shorten the rear output of the NP242 at all.  My NP242 was the early Cherokee style with a slip yoke on the driveshaft and a big rubber boot.  On a tip from Rick/eaglefreek, I got a junkyard driveshaft from a 2WD Grand Cherokee WJ.  It was about the right length but the front yoke was wrong, so I had a shop replace it with the Cherokee style yoke.  I drove my Eagle to the shop with the NP242 in 4HI with just the front shaft connected.  No issues, but I was clenched up the whole time.  I can't swear that they didn't cut the Grand Cherokee shaft down a bit, but I didn't see any evidence of that when I picked it up.  Note that I have a 2" lift in the rear, using helper springs.  Not sure how this would affect the length of driveshaft, check this before you commit.

Shifter:  I briefly toyed with using a Cherokee shifter but gave up quickly.  Too much fiddling around.  I got a Novak SK2X which mounts straight to the TCase and therefore isn't connected to the body at all.  It comes with a long handle you can heat bend into place, and some leeway on where it goes.  If you were very clever you could simply cut a slot for the shifter, but I ended up cutting out a larger access panel.  This made it easier to adjust the shifter and install from above.  Made a mess of my carpet, but it was never that great anyway.  I used a shifter boot from a Jeep CJ I think - just looked online for one that looked about the right size.  I plan to install a bezel around the boot and clean it up, once I get some shop time again.

Feel free to ask any questions.  Here are a bunch of pictures:

This was my Cherokee NP242

Tag, for reference:

Didn't use the Cherokee front driveshaft, but you can see the yoke is the same style as Eagles.

Here is the speedo gear.  Ignore the blue one - that was a Jeep Cherokee unit that will NOT work in the Eagle.  The rest is stock Eagle stuff.  I replace the white gear, and the black housing to fix my speedo ratio.

This was the back of my 998 transmission when I took off my NP129.  The red ring is the stock seal, and the short shaft on my NP242 won't go that far.  You can see here that the seal is installed fluch on the outside, but I found that the pocket is much deeper.

So I got this extension seal from Teraflex.  This pic is trying to show that it will move the seal out about 3/4" from the stock location.

Install the seal extension one micron at a time.  Take your time and do the math to stop when it's 3/4" proud of the original location.  You can overshoot if you are not careful.

This is the shifter I used.  Doesn't mount to the body at all, just cut a slot in the floorboard where you want it.  That upper handle is bendable with a torch.

I think this is a boot from a Jeep CJ.

Go for it and cut a big panel for access.  Save the piece and bolt it back in with some 1-1/2" aluminum bar stock around the seam to create a flange.

I was fighting a deadline at this point, I need to go back and clean it up.  I'll fabricate a bezel, cover the carpet madness.

Couldn't resist...

Immediately after putting in the Np242 I drove from Atlanta to Nashville.  Picked up 2 buddies and their motorcycles, did a speed run to Arkansas.  Got onto dirt and didn't stop for 2 weeks until we got to Salt Lake City.  Without the low gear, I would never have made it up (and down) the 12,000 ft rocky dirt mountain passes in Colorado.

Do it!

This is excellent information. Thank you.  I may have to change out my 119 for 242 after I test drive my car off road.  Fun fact, NP 218's were replaced by NP 242's in humvee's.  IIRC Splines are different from Eagles but still could be adapted.  Speedo is mechanical as well.  Both have hi and low lock with internal cooling loop in series with transmission lines.

Thanks again.

Added: These have no 2 wd fork so they are full time 4 wd .  218 is a fixed bolted output and this 242 is a slip yoke.  These are typically behind TH400 and 4L80E transmissions.  Connected via an adapter plate.

aaawww sweet, thanks amarshall. Ive read through your thread a couple times now and really love what youve done with that thing. Good into on the extension seal and the rear driveshaft, I never would have found that otherwise. I may still do the hack n tap and use the eagle driveshaft though, I like the slipjoint in the middle. Whatever I decide, Ill update this thread with my findings.

Glad I can contribute what worked for me.  I should also do a shout-out to Rick, we compared notes on most of this stuff and he encouraged me to go for it.  Thanks buddy!


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