Bone Jarring Bang!

J

jrowell

NAXJA Forum User
Location
Bakersfield
My heep has started something new. The last 2 trips to the trails it has started doing a BANG about 3 times on the whole trail. It sounds and feels just like the locker unloading. I've had a Detroit front n rear for some time, and have experienced the back unloading. It has happened a couple times a year, always when getting out of a parking spot or something like that… never on the trail in 4low.

This new BANG happens at any given time, has never happened on an obstacle or under load. Not happening on tight turns. Just going slow under 5mph give it a little gas and BANG. Sounds like someone took a big hammer and hit my cage. I can't tell what direction it is coming from.

Could it be the Tcase chain, even though it has never done it under load? It has also never done it on the trail in 2wd.

87xj 4.0, AW4, NP231 (late model style). D30/ D44 both with Detroits. Front axle joints just changed and hubs look good. Front cover opened and everything looks great. Going to take a peak into the rear this weekend.
 
did you pop the covers and inspect the diffs?
broken ring gear teeth or broken spider gears or broken locker.
 
blondejoncherokee said:
did you pop the covers and inspect the diffs?
broken ring gear teeth or broken spider gears or broken locker.
Click to expand...

Front looks good, going into the rear this weekend. My though is… it was one of the diffs, it would do it on the street in 2wd as well?… right?

My thought is Tcase… since it only does it in 4wd… or Springs since it only does it off-road.

but i'm open to other suggestions!
 
Check both, get that crap fixed before Swamp, or you could be "That guy" :)
 
Ya the rear would do it on road, the front would possibly be 4x4 only.
Are you sure its not just your coils getting caught on the frame, track bar mount, bump stops, etc and just catching, binding, then finally un catching off whatever hooked it and unloading in aloud clang?
 
blondejoncherokee said:
Are you sure its not just your coils getting caught on the frame, track bar mount, bump stops, etc and just catching, binding, then finally un catching off whatever hooked it and unloading in aloud clang?
Click to expand...
That is a possibility, although it doesn't have that "springy" coil impact sound. It's a sharp hit and done. I'm going to look this weekend for any wear/ shiny spots on coils and leaf springs.
 
Transfer case chain skipping? Not really sure how to characterize that one (never had it happen that I know of) but it's a thought
 
yossarian19 said:
Transfer case chain skipping? Not really sure how to characterize that one (never had it happen that I know of) but it's a thought
Click to expand...

If that is the case which I doubt there are much bigger issues!!
 
yossarian19 said:
Transfer case chain skipping? Not really sure how to characterize that one (never had it happen that I know of) but it's a thought
Click to expand...

That's on my list of possibilities. I'm not sure if I can reach the chain from the plug, but I'll give it a shot. I would think if it was the chain, it would do it under load on an obstacle. It does it at random times light to no throttle.

I seem to be able to explain away every possibility! Maybe it's just in my head.
 
Opened up the rear end. Everything looked good. no broken teeth or metal in the bottom of the diff. decided to check the ring gear bolts. the first one I checked was little more than finger tight! started to torque it down to 50ft lbs... of course it broke. drilled and easy outed it. spun the ring gear a bit to check more. they are all pretty loose, going to buy a new set. not sure if that is my noise or not, but at least I caught something else from blowing up!
 
If the ring gear bolts where loose its a good probability that was your noise. As the axle flex's a bit it could put a strain on the loose gear and flex it a little. Try it out after you put new bolts and torque it down to spec. See if you can replicate the noise. May also want to check gear pattern and backlash after replacing the ring gear bolts.
 
Had something similar with my xj about a month ago. Mine was popping out of 4lo. Adjusted linkage and no more pops. I did have a heads up because earlier in the day it went right into neutral going up a hill.
 
jrowell said:
Opened up the rear end. Everything looked good. no broken teeth or metal in the bottom of the diff. decided to check the ring gear bolts. the first one I checked was little more than finger tight! started to torque it down to 50ft lbs... of course it broke. drilled and easy outed it. spun the ring gear a bit to check more. they are all pretty loose, going to buy a new set. not sure if that is my noise or not, but at least I caught something else from blowing up!
Click to expand...

That was most likely your problem right there!
 
blondejoncherokee said:
did you check the front Ring gear bolts too ?
Click to expand...

Ya, I checked them and they were good. I changed the front locker within the last couple years… The Rear hasn't been touched in around 10 years.

Although I have recently read that if you re-tighten them at all, it breaks the locktight bond and could lead to them coming loose. Now I'm paranoid and may end up opening up the front and pulling the bolts cleaning and re-locktighting.
 
I put a spartan locker in the front of my jeep several years ago and reused the factory gear bolts. After 3 plus years of offroad driving and beating on them no issues. Just make sure they are torqued to specs and if your that worried back them out one by one add a few drops of blue locktite and retorque 1 by 1 while on the ground or on jacks.
 
jrowell said:
Opened up the rear end. Everything looked good. no broken teeth or metal in the bottom of the diff. decided to check the ring gear bolts. the first one I checked was little more than finger tight! started to torque it down to 50ft lbs... of course it broke. drilled and easy outed it. spun the ring gear a bit to check more. they are all pretty loose, going to buy a new set. not sure if that is my noise or not, but at least I caught something else from blowing up!
Click to expand...

I had the identical description of the noise you are having. Light load, etc. In my case, the rear diff ring gear bolts were loose, but the bang was one bolt at a time shearing. When the last one sheared, I then knew what the problem was!!

Sounds like you caught it just in time. Yes, I'd be replacing every bolt, and making sure the holes weren't damaged, so the ring gear sits flush on the carrier.

David Bricker / SYR
 
So far so good. Took the heep on a run yesterday and not a peep out of the rear. Glad I caught those suckers before the whole rear end exploded.
 
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