If you look at the third picture at the beginning of this thread, it is the inside of the extension. At the bottom right there is a groove cut out of the housing. This groove/channel goes through to the back of the extension where the seal mounts. Is the groove at the bottom when the cone is installed (my son dissassembled it so I'm not sure where the groove was situated). The reason I ask is because when we reinstalled the cone, I put the groove at the bottom and now the seal leaks when the jeep is parked uphill. If on flat ground or parked downhill, it doesn't leak. I was just thinking if the groove wasn't at the bottom, the fluid wouldn't have a path to leak out the back when parked uphill. I did not replace the bushing.
god it's been so long since i did this. IIRC that channel is there for the fluid to drain back to the case and I believe i installed it on the bottom. when you installed the seal did you silicone the outer body where it presses into the tail cone? if the seal is working it shouldn't be leaking past the output shaft regardless of orientation, so I'm inclined to think its seeping past the body of the seal.
I realize this thread has been around for quite a while, and I will check elsewhere/start a new one, but I thought i would jump in and ask this question again, since it doesn't look like it was addressed the first time. Can a slight amount of play in the main shaft on the NP231 cause any driveline vibration under load. I have a 90 YJ, and when the Jeep warms up, it has an annoying vibration from 30 MPH through about 50MPH, regardless of what gear it's in. I have new wheel bearings, ball joints, control arm bushings, sway bar bushings, everything's nice and tight. The problem goes away when the clutch is depressed. The problem goes away when driving in 4WD. Driveshaft checks out perfectly, with new U Joints. Tires are balanced properly and in great shape. Engine and Transmission are new. The ONLY thing I have found is this slight elliptical rotation of the Main slip yoke shaft inside the transfer case when it's in gear. I put the Jeep in gear running with the thing on jack stands, with the rear driveshaft removed. The seal doesn't leak on the tail cone, but this is the ONLY anomaly I can find. I've been suffering this for over 2 years and NO ONE has been able to tell me what it is. Needless to say, it's making me crazy. ANY ideas would be very welcome!
Just finished replacing mine. To get out my seal I managed to grab a hold of the lip of it with a pair of vise grips, twist, and pull it out. If you have the option take your extension housing to an auto shop and see if they can press out the old bushing and push in the new bushing and seal. I took mine to work and the whole process took 5 minutes and most of that was finding something to push out the bushing with. Even if they charge $20 (really high estimate in my opinion) I think it's worth the piece of mind that you aren't risking chipping, scratching or cracking you house while waylaying it with a hammer.
i did this repair yesterday after reading the OP instructions. Thank you very much for the writeup. i have everything back together, including replacing both u-joints on the shaft in about 3 hours ( i am not the best at u-joints, but i finally did it complete by myself - just took my time). Everything went back together correctly and the test drive worked out fine.
This morning i checked under the jeep for leaks and saw none. on an errand i started getting a vibration/shutter after taking off in first gear. It almost seemed like the rear end binding up.
I came back home to find that on the rear u-joint strap - either i didnt tighten it down enough, or it loosened up. Is this supposed to have thread locker on it? i put some on, and re-tightened them down. test drive now has no vibrations.
Once again thank you for the write up, my transfer case was definitely low on fluid and i changed that out also.