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NP231 Tail Shaft Leak Fix

112K views 47 replies 29 participants last post by  kenneymartin 
#1 ·
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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#2 ·
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
 
#3 ·
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
 
#5 ·
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
 
#7 ·
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.
 
#8 ·
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
 
#9 ·
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. :thumbsup:
 
#10 ·
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
 
#12 ·
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
 
#13 ·
#14 ·
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?
 
#16 ·
I believe the 231 changed in 1990 but only in the cherokees and they lost the tail shaft. My 1989 says amc231 on the tag but I have a 1990 transfer case that says np231J and doesn't have a tailshaft so I can only use the chain and internals, thats why I asked where to find the tailshaft.
 
#17 ·
So i followed the post (great job btw) and replaced my seal after finding a leak at the output. I actually found the leak because items i left on the floor behind the seats kept getting damp and i could not figuer out why. Looked underneath and saw that the oil was being splattered up on the underside during rotation. Thought it might be coming up through the seatbelt hold down bolt.

I replaced the seal and u-bolts and put new silicone/tightened the bolts on the extension. I did not put a new bushing in however :(

After that i put about 200miles on the jeep and am now noticing that some of the silicone has fallen out between the extension cone and the housing, and the output seal seems to have backed out a bit (not all the way just a little on the bottom). I am still getting some leaking although i am not sure from where as the drive-shaft is pretty clean near the seal still. Should i look to repeat the process and get a new bushing or am i looking for something bigger that may be causing enough vibration/movment to explain this? Any ideas are appreciated. :confused:
 
#18 ·
I am experiencing a slow drip right out of the seal itself... somone suggested that the output shaft itself may be very slightly worn from the seal if its the original from 93 (which I think it is...) and there is now just enough space for a slow seapage... I am not sure if this is possible but can tell you there is no real "play" in the shaft... although I guess I am not sure what type of play there should be and when its too much. I am happy to say that I tourqued everything up and nothing has backed out - the output shaft extension(tail cone) is dry as a bone...
 
#19 ·
Jaycal3,

Not really sure what 'play' there should be. I know there was alot of movement in the u-joints so i replaced them. kinda thought maybe that was the culprit but nope. shaft seems dry, and cone too. but i see a slow leak and freddy kruger type splatters all over the underside so not sure what to make of it. I guess at the minimum im going to have to clean everything up really nice and try to find it early. before everything starts looking like a murder scene again :D and yep, mine is the original from 89...
 
#20 ·
Output leak fix

Sentinal02, thank you so much for this post; amazing I was just outside doing the exact same thing, but with a new housing...and I am glad I saw you post because I thought I was missing something. (Just an FYI your links to the pics are broken).

Thanks again!
 
#22 ·
This seal is giving me fits

http://www.opiebennett.com/images/Jeep/D4-ford9-swap/Day 15/IMG_3934.JPG

Here is a picture similar to mine, the type with a rubber boot and I have replaced this seal two times. It leaks more than before. The first time the "C" clip just in front of the seal tore the seal. I am still working on the second time. Does anyone have any suggestions or experience with this this seal.
 
#24 ·
I found the answer to my TJ rear seal leak issue. The problem has to do with my install. In my previous post I linked to a picture of the TJ seal, retainer clip and slinger. The retainer clip goes into a groove on the shaft, this groove has been the problem. I went Nogalitoes Gear in San Antonio, the guys there tell me to put some tape on the shaft to cover the groove as I am installing the seal. This will let the rubber portion of the seal glide over the groove, where in the past I had allowed the seal to fall into the groove as I was installing. I felt a little springy action as I was driving seal home, this springy feel was my seal tearing past the groove.

The tape is to be removed once the seal is installed. There is also a $100 special tool that will accomplish this task. I'll stick to the tape.
 
#25 ·
If the bushing is bad and there is a little bit of play in the slip yoke, can it vibrate similar to a bad u-joint? I have a brand new driveshaft, and the driveline angles are OK, but it vibrates terribly.
 
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