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Discussion Starter · #1 ·
Since I had my Jeep it's always rode hard in the back. I figured that was from a combination of a lift and 35s but I don't think that's the case anymore. Now when I go over a speed bump or hit a pothole it feels like the body is slamming on the frame in the back with a hard loud thump maybe clunk combination. Been too cold last couple weeks to really get my hands dirty (no garage). From what I've researched the cause is either u joints or body mounts.

Any suggestions , tips or words of wisdom are greatly appreciated.
 

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See if it still has a track bar in the rear. If it is connected, that will give you the stiffer than stock ride, as well as a likely culprit to the thump. The rubber bushings in the stock bar wear out and allow for the bar to clunk.

Highly unlikely that it is a body mount, since most of them would have to be loose in order for the body to be flexing enough to make noise on a bump, and u-joints wont make a clunking sound in relation to a bump.
 

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Discussion Starter · #3 ·
I will definitely look into the bushings.It doesn't ride rough all the time just over like over speed bumps and the front rides very smooth compared to the back so whatever is hitting is definitely in the back. It's gotten gradually worse over time.
 

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I would not rule out body mounts but I agree with forlife, I had a yj with body mounts that were bad enough to make an awful thump but like he said there were several that were bad. Just give it all a good once over. Maybe have a buddy stand in the back of the tub or bumper n bounce on It a few times.
 

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Discussion Starter · #5 ·
If it is the body mounts I would imagine a couple went bad at once or one was bad and the extra weight made a couple more crap out. Is that common on a yj? I'm gonna start with the easiest thing to check and go from there. not very fun Wrenching when it's 10 below or single digits.
 

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If it is the body mounts I would imagine a couple went bad at once or one was bad and the extra weight made a couple more crap out. Is that common on a yj? I'm gonna start with the easiest thing to check and go from there. not very fun Wrenching when it's 10 below or single digits.
yes it's very possible. There are 11 body mounts total so it's going to take several to fail. How is the rust on the under side of the body? Bushings in shocks control arm and so on are going to be the starting points
 

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Chiming in with what could be the same 'clunk' from the rear when going over bumps. The cold weather also prevents me from checking it out, but next Saturday, 3/7/15, I'll have the jeep up on a lift and be able to get a good look at possible causes. I'll let you know what I find and hope it helps you out.
 

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I had an egged out hole on my lower shock mount that clunked until I repaired it. If the track bar is still on, that could very well be the culprit as well.
 

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I know this thread is over a year old but the newly acquired "thump" in my YJ took me searching for an answer. The track bars (front & rear) are still on but I'll remove them tomorrow. But that being said, I really don't think they are the culprit.

This thump sound is like something heavy hitting the bottom of the tub. It's not enough that the passenger feels anything under their feet, but that's what it sounds like. Anyone have this problem before and if so, what was it?
 

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I know this thread is over a year old but the newly acquired "thump" in my YJ took me searching for an answer. The track bars (front & rear) are still on but I'll remove them tomorrow. But that being said, I really don't think they are the culprit.

This thump sound is like something heavy hitting the bottom of the tub. It's not enough that the passenger feels anything under their feet, but that's what it sounds like. Anyone have this problem before and if so, what was it?
The boggieman
 

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I had a thumping above 55 mph and it was the front differential cent hose banging around. It had come loose from the firewall. Had to shorten it due to damage and attached it to the ps hoses with zip ties. No more thumping or banging on the tub. Good luck!
 

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This isn't a high speed thing, it happens at any speed. And it's strange in that sometimes it will completely go away and the Jeep will be so quiet it scares you. Then a day or so later it starts up again. Sounds like someone is underneath the Jeep, hitting the undercarriage with a rubber mallet every time I hit a bump.

I've not jacked it up yet but while it's sitting in the garage I've shaken everything, exhaust pipes, muffler, etc. Noting is loose.
 

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OK, I found mine. Believe it or not, it was one of the two hinges that hold the hood on. There was some play in the hinge (side to side) and somehow that transitioned down to the firewall and made a "thud" sound. I would never have imagined a small gap could make that much noise but it did.
 
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