98 ZJ rear end noise when coasting, need some ideas (video inside) - JeepForum.com
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Unread 10-31-2011, 01:46 PM   #1
98318242
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1998 ZJ 
 
Join Date: Dec 2010
Location: Olean, NY
Posts: 178
98 ZJ rear end noise when coasting, need some ideas (video inside)

For probably going on 9 months now Ive had a weird noise coming from my rear end when Im coasting. I can be cruising at 30 mph and let off the gas and it's almost like a light buzzing coming from the rear. If I give it the slightest bit of throttle like just a tiny push enough to maintain speed the noise goes away. Yes the faster I go the more louder and high pitched the noise seems to be. I the rear diff fluid was changed a few years back but doesn't even have prob 12k miles on it. I did check it over the summer to make sure it was full and it was but it looked kind of greyish blackish, the grey is what bothers me. Anyways today I was out and about and decided to use my phone to try and get a video of it and when listening to the video on my phone I can hear it, so hopefully once its uploaded to you tube you guys can hear it too. Listen for it and let me know what you think, in the mean time enjoy the exhaust note! Here's a link, sorry I tried the embed link from youtube and my brother and i havent been able to figure out how to embed a video on here from youtube to save our lives. Anyways let me know what you think and the beginning of the video you cant hear anything cuz its a bumpy street but after that you can, and you can hear it hum as I slow down to a stop too.
http://youtu.be/oH4_2TU0UfU

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Unread 10-31-2011, 01:56 PM   #2
PolkaPower
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1998 ZJ 
 
Join Date: Aug 2011
Location: The Abyss, MD
Posts: 16,039
Wheel bearings, rear diff, ebrake or brakes. It's hard to tell in the vid with the radio on. Best thing to do is put the rear on jack stands and disco the drive shaft. Chock the front wheels, release the e-brake and spin the tires and shake the tires up and down, left and right. There should be no movement up and down left or right. See if you can hear the noise either coming from the wheel end or if it's in the diff. Take the tires off, inspect the brakes, take the rotors off and check the e-brake for broken material scraping around. Check the pinon for up and down left and right movement. If you still can't find it, take the diff cover off and drain the fluid. Check for metal shavings and inspect the gears as you spin the tires.
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Unread 10-31-2011, 01:58 PM   #3
98318242
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1998 ZJ 
 
Join Date: Dec 2010
Location: Olean, NY
Posts: 178
I HAVE checked the pinion for play because thats the first thing I thought it might be and its tight and has no movement. You can really hear it humming in the one part of the video when Im slowing down to a stop. Thanks for the advice.
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Unread 11-01-2011, 11:04 AM   #4
98318242
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1998 ZJ 
 
Join Date: Dec 2010
Location: Olean, NY
Posts: 178
Any other ideas? What really stumps me is that it's ONLY when coasting. The tiniest touch of the gas and it's gone. It seems to me if it were brakes it'd go away when I hit the brakes, that makes no difference. Also I've heard the typical 44a howl in my brother's 5.9 he had and that was constant and a much deeper more howling noise almost like a low on fluid noise. I can get another video with no music (duh) and a friend sitting in the back on smoother longer roads if that would help. Thanks again.
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Unread 11-01-2011, 11:37 AM   #5
PolkaPower
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1998 ZJ 
 
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Location: The Abyss, MD
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Maybe the drive shaft since you say it goes away when you give it gas. My wheel bearings whined at all speeds. Also check youtube, I know there are some vids of zj's with bad wheel bearings and rear noises.
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Unread 11-01-2011, 11:47 AM   #6
accord23
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1998 ZJ 
 
Join Date: Jun 2010
Location: Mobile, Alabama
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I have been having the same problem on my 1998 ZJ only that mine goes away when I'm on 50miles/hr or above, and mine comes from the Right rear wheel which makes me thing its the drive shaft. wheel bearing checked ok diff was also good. I just don't know what to do with it.
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Unread 11-01-2011, 03:54 PM   #7
98318242
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1998 ZJ 
 
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Location: Olean, NY
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This had just got me really frustrated. I finally get a job and plan to put some money into the Jeep and its one thing after another now!
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