Will a plugged NP231 vent blow fluid out the rear output seal?

thecarman

Well-Known Member
Joined
Mar 17, 2005
Location
Apex, NC
I was driving my 1997 TJ to a garage this morning to get inspected when it blew a bunch of ATF out the rear output shaft seal on the T-case. I'm trying to figure out what happened. Please see details below.

I just got this thing on the road after having replaced a broken T-case tailshaft housing and bent main shaft (previous owner lost a rear d-shaft on the highway). Installed new rear output shaft seal and slinger. Also installed a hack-n-tap SYE and dual-cardan rear d-shaft.

I test drove it around my place and on some country roads up to about 55mph. No vibes, no leaks. This morning drove I-40 from Burlington to Chapel Hill at 65-70 mph, and just before reaching 15-501 my wife called to tell me the Jeep was smoking (she was following me). Pulled off at the exit ramp to see that ATF had blown out of the T-case rear output seal, and was all over the d-shaft, exhaust, rear axle, etc. Limped it REALLY slow the final 3 miles to the garage for an inspection and left it there. Will pick up with a trailer and haul home (lucky for me I know the guys and they'll go ahead and inspect it for me).

What I'm trying to figure out - what the heck happened? :) Could I have a clogged T-case vent, and it caused the fluid to blow past the rear output seal once the T-case got hot? I know the new (used) main shaft is good and the seal was put in right. The t-case was out of the Jeep for a LONG time waiting for me to fix it, so mud dobbers could have clogged the rubber vent hose, which was left open, still attached to the Jeep (happens at my place all the time to any small hoses left open, like an auto trans cooler line or an air compressor hose).

Any other ideas, while I'm sitting here at work worrying about it until I can get it home and check it out? :) I'm so sick of working on this thing - I hope it's something simple and I don't have to pull the T-case again. :)

Thanks!
Richard
 
yes could happen, typically it will just push oil past a seal (since its spinning). But some seals arnt held in by much...

And your 100% on those damn mud dobbers !!!! bastards cloged every damn opneing on my jeep when it was out side last summer/fall. Evey bolt hole, hose, fitting and other places yet to be found...

glad to see you finally getting that jeep moving again !!
 
Hey Mike!

I am hoping that's what happened. And I didn't mean to imply that it blew the whole seal out - just blew fluid past the seal. (I just edited my post for clarity.) I can't see the condition of the seal because the metal "slinger" is covering it. Can't wait to get it home and check it out!

This is the one time that I actually *hope* mud dobbers have clogged a hose, since that wouldn't be too hard to fix. :)
 
If I remember correctly the vent has a vented cap on it that is suppose to keep stuff out of it. The smoke was probably coming from fluid being slung on the exhaust. Sorry can't help you on the reason why it's leaking.
 
ya id say thats all it was then... typically the rear is worn out the most as it subjected to the most dirt/grime. And the easiest to leak... I'm not sure of the layout on a stock TJ w/ an auto but just keep in mind some may have also pushed through the front/input seal either into the open area between the t-case / tranny or into the tranny, neither is prolly to big of a deal, just might leak out later on...

BTW: I always pull those shields off, much easier to keep clean and inspect.

-mike
 
yager said:
BTW: I always pull those shields off, much easier to keep clean and inspect.
Click to expand...

So I don't need to run that "slinger"? Just leave it off so that the rear seal is exposed?

If I can leave it off, that's fine with me - the slinger sucks to take off. :)

Brought the trailer to work with me today, so will be getting the Jeep home after work tonite.
 
Got to work on the Jeep this weekend. Pulled the vent hose, and could not blow through it. Took the filter off the upper end of the hose, and could blow through the filter but not the hose. Pulled the whole hose, and a bunch of mud-dobber nest/dirt blew out. Freakin mud dobbers!!! Also found that they had made a nest inside the muffler of my weedeater! :)

Anyway, put the cleared vent hose back on, but the rear T-case output seal still leaked. Pulled the slinger, and found a piece of the inner sealing lip OUTSIDE the seal. Pulled the seal, and yep, the inner seal lip (the one with the spring around it) was half missing. Nothing had rubbed on it or cut it. Looked like pressure inside the T-case pushed on the seal until it folded the lip under, a piece of the lip broke off, and the pressure pushed that piece (and the fluid) through the outer lip of the seal. So it does look like it was a clogged vent causing pressure build-up thing - I can't see how anything mechanical would have caused that. Also, it only lost about 1/2-quart of fluid, so I was relieved to see that there was still some fluid in there so it's not like it ran dry.

Put in a new seal and test-drove the Jeep - no leaks. Next test is a long highway run (since that's when I experienced the problem in the first place), but I'm going to hold off on that until I finish beefing up the rear leafs in my Suburban this week so I can tow the Jeep home if it breaks again. :) I don't feel like having to borrow a tow rig AGAIN to get the Jeep back to the house. :)

Later!
Richard
 
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