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NP231J transfer case occasional poping noise

D

dennis461

NAXJA Forum User
Location
Waterford Township, NJ
I was in deep sand this week on the beach in NJ.
I have wide, 33 inch tires, not exactly matched but real close in size.
I was not getting stuck, and due to speed restrictions, I was just giving it a little throttel to go maybe 1015 MPH.

My 1991 XJ made an occasional pop in 4-low.
I would drive another 100 feet than pop again.

Sounded like a manual transmission jumping out of gear, but I have an Auto-6 cylinder.

I switched to 2-high and got the same noise.
The rear driveshaft has brand new u-joints that I put in, nothing loose back there.

Could the planetary gear make that kind of noise?
 
No problem with disconnect.
Works fine, opened up and no evidence of skipping in there.

Now trying to find a replacement transfer case.
Nothing local :-(
Mine is NP231-J .
6-cylinder automatic
23 spline
vacuum connections at rear of case, not in front.
 
Any idea how much the chain is worn/stretched? Put it in 4wd, jack one front tire up off the ground, and try turning the front driveshaft. See how much rotational play is in it - that will tell you how much the chain has stretched. If you can't get a good feel for it pull the fill and/or drain plugs (fill plug first!!) on the transfer case and feel for looseness in the chain with your finger.
 
dennis461 said:
No problem with disconnect.
Works fine, opened up and no evidence of skipping in there.

Now trying to find a replacement transfer case.
Nothing local :-(
Mine is NP231-J .
6-cylinder automatic
23 spline
vacuum connections at rear of case, not in front.
Click to expand...
The vacuum motor and associated parts can be fine but if there's a leaky switch on the TC or a problem anywhere in the plumbing, it will let go under low vacuum conditions such as the top of a hill, etc. Not the only thing that can go wrong, but it's worth a very careful look. If you can make it misbehave, try running vacuum directly to the pull-on nipple of the disconnect and see if it changes anything. If the "4WD" light goes on at all when it shouldn't, this is a direct indication of vacuum issues, but don't assume the best if it doesn't come on. It'a a nasty setup.
 
i got the same problem agin. first time it was my chain stretched enuf to touch both sides at the same time. just got anoth new one just gota install. but it can also be the mode or range fork messing up of the pads have worn enuf to not hold it in rite under load
 
Split the case and found this spring clip laying in the bottom...
np231inside2.jpg
 
so get it all back together the rite way and check y ur mode fork is moveing to much. check ur secktor guide for play and if ur spring is weak that keeps tension on the fork rod.
Photo0243.jpg
old chain
 
All that stuff you folks mentioned look good.
Plastic tabs look like new.
Shift fork is tight and rollers roll.

Near as I can tell, when that clip came out, if let go of two of the synchronizer tabs (2 of 3 movable steel ones, not the brass).
Found them on the magnet.
They must have forced the steel ring far enough to hit the chain.
The chain pins got pulled out slightly.
Now the chain appears too wide.
When I push all the play to one side, I measure 30+ mils in between the outside link and the next one in.

I don't think I can buy the spring clip by itself.
 
You can get a decent used case for 100 or less on here... usually 130 or so at the junkyard at least in central mass.
 
Here is a pic of the internals...
Look closely and you'll see the inner edge of chain chewed up.
Got a good deal on a Wrangler transfer case from CHris in PA, drove 60 miles to get it.
He knows Jeeps and had a quality case at a much better price than what I was finding (or should I say not finding).


toreupXJ.jpg


Early Wrangler has some differences.
Vacuum switch location,
linkage arm
I'll reuse my XJ tail section

wranglerearly.jpg


Two styles..
GEDC0534.jpg
 
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