thump in the rear

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  #1  
Old 12-04-10, 01:25 PM
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thump in the rear

My stepson has a 2002 jeep liberty. He's been complaining about a noise in the rear for the last couple of months. It only happens in reverse [maybe only when turning] It's difficult to duplicate it as it doesn't happen every time.

It sounds like a box or something in the trunk that is turning over
I checked his jeep out a month or 2 ago and couldn't find anything amiss. The brakes are good, no excess play in the axles or driveshaft and the differential is full of oil. Today was the 1st time I personally heard the noise. Any ideas?
 
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  #2  
Old 12-04-10, 02:26 PM
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1. seriously, there might actually be something in the trunk that does this. modern cars have all kinds of little nooks and niches. i'd start with emptying EVERYTHING from rear.
2. any chances of getting it up on a lift and putting into reverse?
3. loose spare tire?
4. something got caught between rear axle/wheels/underbody? buddies once put a lug nut inside guy's metal hubcap. dude tore half car apart chasing the metal knock. driving - no noise(centrifugal force kept it against the rim), going over potholes, tracks, bumps - ding-ding!
5. it's a rear wheel drive, right? as there's differential back there then, ya know.
 
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Old 12-04-10, 02:26 PM
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The only thing I can think of is the goofy stuff......loose spare tire, jack handle or jack body, bottle of antifreeze, or other stuff loose in the spare tire cavity. Hopefully it isn't a missing gear tooth on his chunk. But only in reverse, doesn't wash that theory.
 
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Old 12-04-10, 04:12 PM
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You have to rule out a trunk monkey issue first. Click below. If the trunk monkey checks out then you (seriously) have to check for any worn out bushings involving any part of the rear suspension. When checking for a worn bushing problem youíre looking for spots where the rubber bushing has worn out and now itís metal against metal.

YouTube - Trunk Monkey
 
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Old 12-04-10, 04:44 PM
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Rear Disc Brakes?????

The parking brake shoes are inside the rotor "HAT" . if a lining were to dislodge from the shoe, it would cause an intermittent "Thump" or "Clapping" noise in reverse ONLY.....

The only problem I have with the bushing theory, is .....If it flexes backward, it must also flex forward in an equal amount. If it knocks around in reverse, it should knock when returning to its normal position, after being flexed in the opposite direction.
 
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Old 12-05-10, 04:29 AM
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The jeep doesn't have a trunk and the spare is mounted outside but I didn't think to check the compartment where the jack and lug wrench are. I don't think that compartment has ever been opened - he bought the jeep new and it has about 88k on it. I'm pretty sure it just has drum brakes in the rear but I'll have to double check. I like the idea of getting both rear wheels off of the ground and then putting it in and out of reverse but I'll have to see if I can get his brother or one of my sons to help......... and hopefully get some warmer weather It's supposed to be below freezing most of this week
 
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Old 12-05-10, 06:51 AM
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I tend to agree with Unclediezel with the brake thingy. My Ram has brake in a hat parking brakes and it can happen. BUT, even with standard rear drum brakes, a spring could break or lining become loose and it would only thump in reverse.
 
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Old 12-05-10, 07:20 AM
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I checked his jeep out a month or 2 ago and couldn't find anything amiss. The brakes are good, no excess play in the axles or driveshaft and the differential is full of oil. Today was the 1st time I personally heard the noise. Any ideas?
Just for Info.......ALWAYS CHECK FOR YOURSELF. Until you have seen first hand that the brakes are good, dont count on it......
This is the pefect example....You arent sure if the brakes are drum or disc....But you stated they were good....How do you know they are good????

Always look for yourself......

Having said that....If they are drum brakes, removing the drum ...say for a safety inspection.....When re-installing it , it MAY cocievably not sit flat on the axle flange. Tighten the lug nuts, and the drum sits at an angle. This can also cause a noise or "Shudder" in reverse only.

U-joints are another place to look......They wear on one side of the cap, primarily because you spend FAR MORE TIME, in drive, than reverse.
 
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Old 12-05-10, 07:44 AM
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I made all the checks myself, I just can't remember it all
I do all the maintainence on his jeep. He's not the least bit mechanically inclined. I'm pretty sure it had drum brakes on the rear and I would have pulled the drum to inspect. When it was 1st brought to my attention, I checked everything I could think of and found no issues. At that time I couldn't not duplicate the thumping sound. I drove his jeep yesterday and heard the thump for the 1st time. I tried pulling forward and backing up again but that would not repeat the thump it sounds like a heavy box or jug turning over but there is no such item in the back of the jeep.

I intend to set the rear end on stands and see how it does going in and out of gear but I don't want to do that until I can get one of the kids [that is mechanically inclined] to help....... and did I mention, it's cold outside
 
  #10  
Old 12-05-10, 08:09 AM
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noise

An other thing that can make a noise is where the drive shaft goes in to the trans. Sometime these get sticky and the noise travels down the drive shaft. Lubing them up can help. This is a long shot,but those are the ones that elude detection.
 
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