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Unread 05-17-2008, 07:26 PM   #1
nicksbar
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humming sound

I just got my 4" rough country kit on my YJ. At the same time i had my diffs changed for a D30 and D35 with 4.10.

I now hear a humming noise when i have my foot on the accelerator.
Starts at about 10mph
When i let off the pedal the noise goes away

Ideas?

Thanks
Nick

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Unread 05-17-2008, 07:35 PM   #2
blue1989yj
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Did you put new tires on with the lift?
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Unread 05-17-2008, 07:37 PM   #3
nicksbar
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yup 33's...but as soon as i let off the gas pedal the noise stops.
So its not a hum from the tires
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Unread 05-17-2008, 07:40 PM   #4
blue1989yj
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Sorry. Wasn't sure. I have MT's on mine and they start humming over 10 MPH.
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Unread 05-17-2008, 07:53 PM   #5
jrollings
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sounds like a problem on the drive side of the ring and pinion but not sure
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Unread 05-17-2008, 08:04 PM   #6
ghost183
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Quote:
Originally Posted by jrollings View Post
sounds like a problem on the drive side of the ring and pinion but not sure

x2...

im assuming you checked the oil level in the rear?

but it could be the rear is "off shim",... if the rears were manipulated at all the backlash might be off, allowing the pinion to shift away from full contact on the ring gear, hence the humming when under power

is the pinion seal sweating/leaking?
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Unread 05-17-2008, 08:34 PM   #7
nicksbar
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wouldn't the hum be constant if it was the bearing of diff?
the drive shaft is constantly turning

how would i check for proper shimming?

i did not install the diff, so i wouldn't know if the oil level is good
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Unread 05-17-2008, 09:02 PM   #8
ghost183
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Quote:
Originally Posted by nicksbar View Post
wouldn't the hum be constant if it was the bearing of diff?
the drive shaft is constantly turning
if it was a bearing ...yes,but im thinking its the shimming of the pinion.. maybe someone rebuilt the rear and didnt shim the pinion right,or assumed the shims he took out, would be the shims he put back.. not so.....

only under power is the pinion trying to rip away from the ring gear.. the driven force from the pinion against the ring gear is a twisting force due to the angle of the cut of the pinion gear, hence it trying to twist away from the ring gear under power, under de-acceleration or coasting, the effect would be reversed and the ring gear is trying to pull the pinion in close, again, due to the twist of the cut


as far as shimming, you need specified tools to set the backlash on the ring and pinion..

but... the FIRST thing you should do , is check the oil level!!

best way to do this is lift the rear of the jeep to get the pinion at a level angle, or close to it, then pop the plug off the diff cover, if oil comes out, youre good.. if not, fill till oil seeps out.. then quickly put the plug back

but im suprised you didnt check the oil level yet
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Unread 05-17-2008, 09:36 PM   #9
nicksbar
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i also read that a bad fuel pump has the same symptoms

Also assuming it is the shimming of the pinion...can i drive like this?
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Unread 05-17-2008, 10:32 PM   #10
BamianYJ
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All of the above very well could be right, but i know when i put on my 33's, i had a humming start but after a little wear it discontinued.
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Unread 05-18-2008, 06:27 AM   #11
jrollings
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i think i would take it back to whom ever performed your regear after you check the oil level.
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Unread 05-18-2008, 07:55 AM   #12
nicksbar
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it wasn't really a re-gear....it was remove my diff's and install diff's from a 4 cyl YJ
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Unread 05-18-2008, 02:22 PM   #13
nicksbar
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could driveshaft angle cause this??
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