ZJ Rear End Whine at 40+ MPH - JeepForum.com
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post #1 of 4 Old 07-12-2005, 01:11 PM Thread Starter
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ZJ Rear End Whine at 40+ MPH

I just picked up a used '94 Limited 6cyl last week. It's in really good shape, other than a whining sound coming from the rear end.

The sound is constant, not pulsating. It can't really be heard until about 40 MPH. From there, the pitch of the sound increases with speed. It's not a grinding or mechanically violent sound; it's a constant tone. The sound is loudest when cruising. It goes away when coasting with my foot off the gas, and gets quieter under acceleration or going up a hill. It's definitely coming from the rear axle area, not transfercase or tranny.

I drained the fluid fromt the rear diff and put in some synthetic 75W90, but the sound is unchanged. The old fluid looked pretty good, though there was a bit of fine gold colored flake in it. The diff gears didn't look worn at all.

I figure the problem must be in some rotating part in the rear end. I'm loathe to take this to a Jeep dealership, as I'm sure they'd want to charge me $79384754 to rebuild my entire rear end. I've seen talk of a pinion bearing...is this the input bearing to the rear diff? Could driveshaft u-joints be making this noise? There are bearings in the diff for each axle, right? What's on the wheel end of the axle - a sealed hub assembly, or a replaceable bearing? Anything else I should look at?

Any input/suggestions greatly appreciated.

- Brian

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post #2 of 4 Old 07-13-2005, 06:47 AM
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Join Date: Nov 2004
Location: Charlottesville, VA
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I have a noise similar to yours emminating from what seems to be the rear (Driveline noises are funny). I dont know the root cause but I did notice today that I did not start getting the Hum/whine until I had been on the road for about 10-15 min. Could this be a heat issue either in the TC or one of the Diffs?

I have also read on here that the cause of the whine is the pinion bearing. I believe that it is contained within the gear assembly inside of the pumpkin.

2005 Grand Cherokee Limited
5.7-L V8 Hemi MDS 330 hp QuadraDrive II with ESLD
All the goods....Tow Pkg, SmartBeam, DVD, NAV, Rain Sense wipers

Finally installed: 18" JK Gladiator Wheels/Tires, RR2.5" Lift
SOLD: 1996 Grand Cherokee Limited Kevin's 2" BB 265/70R16Geolandar AT+II
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post #3 of 4 Old 07-13-2005, 01:17 PM Thread Starter
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I don't really hear the noise either, until the jeep is warmed up a bit. I'm going to try changing out the wheel bearings since those aren't too hard. I wonder how difficult a job the pinion bearing is?
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post #4 of 4 Old 07-13-2005, 06:45 PM
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Join Date: Jun 2004
Location: Buffalo / Brewster NY
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I would deff get this checked out / fixed asap. I bought my jeep with a rear end noise thinking it was just the pinion bearing (got a good deal on her too). Turns out the dood that ovned it before me drove it for 29K + miles with the whine / grind. This killed the carrier and I had to put in a whole new rear end. Just got her back a few days ago. I got some pics and will post them soon.

The pinion bearing is also a rather big job as you take all the guts outta the diff and theres some special procedure for setting up the pinion bearing.

'97 ZJ Laredo
- 4.0L
- 176K, runnin like a champ

'06 G35 Coupe 6MT
- A bit faster than the ZJ
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