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Unread 05-05-2004, 09:55 PM   #1
sentinal02
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NP231 Tail Shaft Leak Fix

Ok, as most of us who have the NP231 transfer case have found out at some point in time, the rear seal where the slip yoke is is prone to leaking. When it gets bad enough, the ATF inside the case leaks out onto the driveshaft and is in turn flung up against underbody of the jeep creating a nice grease slick. While it’s great rust protection, this slick burns against the muffler and we all know that topping off the case once a week gets to be a hassle. The good news is that changing this seal is easily accomplished and is a cheap fix. (under 20 bucks in parts) You don’t even need to jack up the jeep. Here’s how.

As I just mentioned you don’t need to raise the jeep to do this fix, but if you want some extra room to work in, feel free. The first step to this project is to drain the t-case of fluid. Easy enough if you have a 30 mm socket. If you don’t have one, get one. Those drain plugs are a pain to get at with a wrench and there’s no sense rounding them off trying a tool that isn’t quite the right size. A piece of flashing formed into a trough, or a wide mouth funnel will help keep the fluid from dripping all across the cross member and everywhere but your drip pan. Once you’d drained the fluid, remove the rear drive shaft. Do this by unbolting the straps holding the u-joint to the rear axle pinion yoke. These bolts were 8 mm on mine. Once the straps are loose, the u-joint may just drop out (depending on how clean it is) so watch it. Those bearing caps can come off pretty easily and then you’ll be left looking for all your needle bearings. Not fun and more often then not you’ll end up buying new u-joints because you can’t find them all. Incidentally, you may just want to change out that joint while you’ve got it out. If the drive shaft doesn’t want to drop out, a few taps with a rubber mallet will knock it loose. Put your pan under the slip yoke (where that leaky seal is) and gently pull the rear drive shaft out of the t-case. You may or may not get fluid dripping out, depending on how well it drained.

Once the shaft is removed, locate the 3 bolts holding the rear extension housing to the main part of the case. That’s it, only 3 bolts. If I remember right, they were 15 mm. Crack them loose and remove them. Once the bolts are out you can remove the extension housing. It’s siliconed on there so the rubber mallet may be needed here too. (If you’re using a regular hammer, remember that the case is just aluminum. Don’t go hitting it too hard). Once the housing is off, you’re done under the jeep for now. Take your parts to your work bench.

Here’s a shot of the entire case on the bench with the housing removed.



There’s two parts that you are interested in for this fix. The first is obviously the real seal. The less obvious one is the bushing just behind the seal. This bushing has a tendency to wear out, allowing your drive shaft to move laterally while it’s spinning. If it wears too much, then the seal won’t work properly and you could replace it 7 times and still have leaks. Since it’s a $9 part, it pays just to replace it along with the seal as long as you’ve got it torn apart. Leave the bushing alone for the moment and focus on the seal.

As you can see from the pic here, mine was pretty far gone.





Getting the seal out can be a challenge for someone without a seal puller (me), but it can be done. What I found worked best was to take a pocket knife and work the edge into the lip of the seal where it meets the housing on the side. I’m afraid I didn’t take any pictures showing where I mean, but if you have the new seal then you can see what I’m talking about. Once you have a bit of a gap there, take a screw driver and work it around the entire edge of the seal, trying to push it out of the housing. Most likely though the lip of the seal will bend before it comes out. Don’t worry about that too much. Once you’ve got the lip lifted, Slip one of the ears of the housing (the flare around the bolt holes) into a vise, seal end down. Tilt the housing so the end with the seal is touching the vise to it doesn’t spin. Take a long, heavy screw driver and slip it done the inside of the housing and put it against the inside of the seal. Try and tap the seal out from this direction. Unfortunately, this didn’t work for me either. In the end, I ended up totally mangling the seal, bending the lip almost double before the tension gave enough that the seal could be pulled out. It took a good half hour of fighting with it before I got it loose. Just keep at it and don’t be afraid of bending the seal. As you can see, mine put up quite the fight. The top right part of the seal shows where I bent it over to free it up.



See part 2

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Unread 05-05-2004, 09:57 PM   #2
sentinal02
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Part 2

Just be careful not to bend/chip the housing or put too many scratches into it. All set? Good, now for the hard part.

Yes, the bushing is even harder then the seal. Maybe I was using a socket just a hair too big, but for whatever reason driving that old one out was tough. For me, the 30 mm impact socket that I had for taking the drain plugs out was just the right size (coincidence?) to drive the old bushing out. I recommend taking a dial caliper to your new bushing’s OD and comparing it to whatever you have to drive out the old one. Make sure the driving tool is definitely smaller then the new bushing so you don’t make the bore of the housing wider in the process. Do that and you’re going to need a new housing. To help ease things along, I generously applied assembly grease to the socket after shining it up using 150 grit sand paper. I stopped about 4 times to drive the socket back out so I could re-apply the grease. Even so, I needed a 3 lb sledge to help drive the I strongly recommend putting the housing on a piece of hardwood on the floor or the ground to minimize the amount of recoil you’ll be getting after each blow. A dead blow hammer would have been nice to have as well. I put the socket on a 3” extension so I had a handle to steady the socket. Here you can see the bushing about halfway out. The socket I was using is in the background.



Just keep hammering away and eventually the bushing will drop out. Don’t throw it out yet. You’ll want to use it to drive the new one in. Drive the new one in like you drove out the old one. Use either the assembly grease (the kind that breaks down in engine lubricants) or ATF to lube the new seal before driving it in. You can do this using a bearing press as well if you have access to one.

To put the new seal in, lube the seating surface of the housing and find something that will fit nicely between the outer wall of the seal, and the inner rubber. I found that a 2-1/8” OD muffler union fit the bill nicely, but check yours out while you’re at the part’s store as each seal is probably slightly different. The union will give you a nice uniform circle you can use to tap the seal into place. Tap the seal down into the housing until the seal lip is seated against the rim of the housing.

Almost done. All that’s left is to reinstall the housing onto the main case. Clean up the old gasket material and run bead of silicone gasket maker along the mating surface of the extension housing. Don’t forget to go along the inside of the bolt holes (between the hole and the main bore of the housing) or else they’ll leak. Slip the housing back over the output shaft on the case and reinstall the three bolts, using blue lock-tight. Tighten the bolts to 30 ft-lbs. Reinstall the rear driveshaft (you did change that u-joint right?) giving the silicone time to set up, and top off your case with Dexron II or III ATF. Drive it around a bit and then check for leaks. There shouldn’t be any. If there is, chances are your driveshaft is a bit worn and changing the seal again won’t help. Look into getting an SYE.

All told, the fix probably took me about 2 hours to do. But then it’s hard for me to tell since I was doing a lot more to the case then just this seal. As you can see from the pictures, I was leaking from the speedometer cable adaptor, the bottom of the case from the seal at the halves, and also the front output seal. The front seal by the way is pretty much the same as the rear to change, without the bushing or the housing to remove. It’s harder to get out though since you’re not removing the shaft and have to be careful not to slip into the bearings. I had pulled the entire case out to fix all these leaks but really it probably wasn’t necessary. It was more of a hassle getting everything out and back under the jeep then changing the seals was so if I had to do it again I would probably leave the case attached to the tranny. Start to finish my fixes took about 21 working hours to do and half of that was taking the case out and putting it back in.

Now to sum this up here’s the parts numbers you’ll need:

Rear output seal: Mopar #’s 8350 3126 (87-90 Jeeps) or 4638 904 for 91-95 models. And for XJ readers 4798 117. These seals are very similar and hard to tell apart so be careful if you’re getting them somewhere besides the dealer. I picked up mine at Advance Auto Parts and had no problem but have heard of guys having problems with getting the wrong seal.

Bushing: Mopar # J813 4490 (same for all models.) I picked this up from quadratec, and their number is 52201.01

Any questions, PM me or shoot me an email at silentsentinal@yahoo.com
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RIP: '88 YJ 2.5L Ax-5 NP231
Posi-Loked. Herculined. Optima yellow top. 1" Shackle, 2" BDS. Cragar 397's Aussie front.

92 YJ 4.0L Ax-15 231
5" springs, 1" shackle 31's or 35's depending on my mood
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Unread 09-11-2006, 12:38 PM   #3
bartalo
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Hello 2 all members
I want to thank U for helping me to fix my np231 rear oil leak.
Its very clear instructions and allmost solve my problem.
How can I install the new bushing safely and dont damage it?
Thanks

oren
Israel

Storm-240 (the Israeli version for the Wrengler Jeep) 1992
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Unread 08-11-2008, 05:15 PM   #4
drew2000
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Thanks for the great post - helped me out a lot! I replaced the bearing, seal, and U-Joint this weekend.

Drew
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Unread 08-27-2008, 11:07 AM   #5
jdarg
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You shouldn't really have to drain the fluid. I've done it without doing that and not more than a cup of fluid came out - just be ready for it.

I've also cracked a tailhosing prying the seal out with the right tool and not a lot of effort so be careful. If you can't afford to be down waiting for parts you might want to buy an extra tail housing before you start and return it afterwards. They seem to be made of a pretty chintzy aluminum alloy.

-jd
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Unread 06-05-2009, 03:04 PM   #6
NMYJ
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Is it really necessary to replace the bushing if your just after the seal?
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Unread 06-05-2009, 03:55 PM   #7
sentinal02
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Quote:
Originally Posted by NMYJ View Post
Is it really necessary to replace the bushing if your just after the seal?
technically no, but the bushing is what the slip part of the shaft rides against and if it's worn then the shaft can "wobble" in the hole, possibly causing the new seal to fail. since you're in there anyway it's one of those $10 parts that you should change out anyway just to be sure.
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RIP: '88 YJ 2.5L Ax-5 NP231
Posi-Loked. Herculined. Optima yellow top. 1" Shackle, 2" BDS. Cragar 397's Aussie front.

92 YJ 4.0L Ax-15 231
5" springs, 1" shackle 31's or 35's depending on my mood
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Unread 06-07-2009, 06:28 PM   #8
Goobersbro
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so do you just recomend like black rvt as the gasket maker??? and do you know the napa/reibes part number by any chance I just went and picked up my seal but not sure if they gave me the right one the part number on mine though is 15047

here is a picture of my seal I just bought


if that is the correct seal the Napa part number is NOS15047 it cost 7.99 without tax
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Unread 06-07-2009, 07:57 PM   #9
sentinal02
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Quote:
Originally Posted by Goobersbro View Post
so do you just recomend like black rvt as the gasket maker??? and do you know the napa/reibes part number by any chance I just went and picked up my seal but not sure if they gave me the right one the part number on mine though is 15047

here is a picture of my seal I just bought


if that is the correct seal the Napa part number is NOS15047 it cost 7.99 without tax
RTV is fine as the gasket maker. blue red or black, just pick a color. no idea on the seal number unfortunately. it's been so long since i've done this and now I'm running an SYE so i can't even go out and measure. if you punch the second seal number into their interchange search engine though it brings back this part number for the rear output seal: NOS 14978. using the earlier seal number though don't bring back a match so take that with a grain of salt. comparing the two, it looks like the ID of the seal's are the same 1.5" for the drive shaft, but the OD's are different. if your current seal goes is really hard to the point you can't get it to seat, you might want to try the other seal since it's slightly smaller on the OD. your current width though is nearly double the other seal, so who knows. if it works out for ya, post back so we all know.
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RIP: '88 YJ 2.5L Ax-5 NP231
Posi-Loked. Herculined. Optima yellow top. 1" Shackle, 2" BDS. Cragar 397's Aussie front.

92 YJ 4.0L Ax-15 231
5" springs, 1" shackle 31's or 35's depending on my mood
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Unread 06-08-2009, 05:13 AM   #10
Goobersbro
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yea this is what I came up with


Part# NOS 14978
I.D. : 1.5000"
O.D. : 2.3760"
Width : .3750

Part# NOS 15047 the one I have

I.D.:1.5000"
O.D.:2.3830"
Width:.8150"


hmm well I guess I can try and see if it works and if it does great if not Have to buy another one.

The O.D is dang close but the width is way off
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Unread 08-24-2009, 11:56 AM   #11
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Oh My, I have this problem too, noticed it yesterday.

The Jeep is starting to cost me a bundle in maintenance.

Suppose anything will eventually. Thanks for the write up I'll give this a try down the road.
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Unread 09-06-2009, 10:08 AM   #12
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Hey guys great post. I have a big problem and hope someone might be able to help. Does anyone know where I can buy the 3 bolt tail section on the 87-90 np231 or a part number? My U joint broke and while the driveshaft was beating the hell out of my floor and muffler it also broke my tail housing.

thanks for any help
Brett
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Unread 09-06-2009, 10:24 AM   #13
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Quote:
Originally Posted by Phoenix916 View Post
Hey guys great post. I have a big problem and hope someone might be able to help. Does anyone know where I can buy the 3 bolt tail section on the 87-90 np231 or a part number? My U joint broke and while the driveshaft was beating the hell out of my floor and muffler it also broke my tail housing.

thanks for any help
Brett
Original Replacement Parts 83503156 - Rear Extension Housing for 88-99 Jeep Wrangler YJ with NP 231 Transfer Case - Quadratec

That????????
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Unread 09-12-2009, 08:35 PM   #14
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ok that sounds great and all but i got a question. im doin some work on mine right now cuz it kinda...exploded on me. so i have to replace it. however mine doesnt have that houseing your talking about mine has a rubber boot. is there something wrong or is it just a different type of 231?
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Unread 09-13-2009, 08:39 AM   #15
jaycal3
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Rubber boot? Does your have the seal already installed? A pic would help... unless I am the only one not understanding...
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