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!
Topic: hooped transfer case / np242 swap discussion (Read 13292 times)