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Unread 12-06-2012, 05:08 PM   #1
ZJMatt
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1998 ZJ 
 
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Location: Weare, New Hampshire
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"Moaning" noise in 2WD

My jeep recently started making this noise when accelerating or climbing hills. It's a very low pitched whine/whirr - almost like a moan.

As of last night, I'm also starting to hear it when decelerating. Rather than being a somewhat continuous pitch, you can hear it "wind down."

The noise is pretty loud in 2wd especially when coming into a hill. For hoops and giggles last night I put it in 4-HI for a bit on the pavement, and the noise was barely audible.

In the first video, you can hear it start around 7 seconds, about the time it shifts.


When taking this video I started off on a steep hill which mellowed out then went up again. The noise was very loud in the jeep, but for some reason didn't really get picked up in the video until around 37 seconds.





Just as an obvious disclaimer, I am not talking about the sound of my exhaust, or air coming in my sunroof.



My guess is a U-Joint or bearing in the rear diff? When I shift into 4WD it's splitting the power between the front and rear so there's not as much stress on the rear drivetrain, making the noise go away?


Thought I had this listed in my proifle but guess not.
1995 ZJ with the 4.0, 42RE, NP231, D30/D35. 218k miles.

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Unread 12-09-2012, 11:18 AM   #2
ZJMatt
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I drained and refilled the front & rear diffs the other night. Took it for a test drive. First time accelerating it still did it, but after a little bit it stopped. Yesterday I went out, and it was on-and-off. Sometimes it would howl, sometimes it would be quiet.

All the gears in both differentials looked good and there were no chunks in the bottom. Fluid was nasty when I drained it but at a decent level.
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Unread 12-09-2012, 11:32 AM   #3
BLarkin
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From what you describe, sounds like classic bearing noise in rear diff. Like you said, when you split the power in 4HI, less pressure on rear diff, therefore noise is quieter.
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Unread 12-09-2012, 11:48 AM   #4
ZJMatt
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Quote:
Originally Posted by BLarkin View Post
From what you describe, sounds like classic bearing noise in rear diff. Like you said, when you split the power in 4HI, less pressure on rear diff, therefore noise is quieter.
I understand the pinion seal is a very easy fix (mine is leaking, so might as well do it), but what about the bearing? Do I have to pull the carrier? Have the gears reset? Or can I pull the driveshaft and get right at it from there?
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Unread 12-09-2012, 11:58 AM   #5
PolkaPower
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If it's like a metallic shhhhhhhh with a slight roar sound then it's probably a bearing issue. My carrier bearings in the rear diff would get louder with distance driven after it heated up really good. I drove it like that for almost a year until the sound became unbearably loud.

Where do you think the noise is coming from?
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Unread 12-09-2012, 06:20 PM   #6
Insane_Jeep
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i'm having the same issue, mine is most noticeable right at 60mph...part throttle its the loudest...

hopefully after the new year i'll run it to the local shop that has some really good old guys who do good work on rear ends and suspension...(also need shocks and some bushings up front)

but i've been told it was also a bearing in the rear...
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Unread 12-10-2012, 12:03 AM   #7
ZJMatt
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There is no Metallic "shhh" sound, just a howl/roar/moan (whatever you want to call it).

If this is a bearing issue, is there any harm in continuing to drive? You guys don't/didn't seem too hurried to get yours fixed. I only drive my jeep about once a week 50-75 miles now, just to "keep things fresh." Ironically, this started happening not long after I retired it as my daily driver. However this Friday I'll be putting about 200 miles on it. I don't care if it gets louder - I can turn the radio up more. But what would happen if the bearing fails completely? Could it send chunks into my gears? Lock up my rear end? Or will it just keep whining until I replace it and I shouldn't worry?
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Unread 12-10-2012, 07:49 AM   #8
PolkaPower
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Yes it could screw up the diff if it comes apart totally. No way of telling when that will happen. During that year when mine was failing I took it out on 8 hour wheeling trips all over plus another 45 minutes of highway driving. Probably stupid but luckily nothing crazy happened. I had the bearings replaced and they found that my limited slip was coming apart. The metal that I was finding in the housing was from the thrust washers coming apart. They rebuilt that too. All together it was 700 bucks.
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Unread 12-10-2012, 03:44 PM   #9
ZJMatt
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Quote:
Originally Posted by PolkaPower View Post
Yes it could screw up the diff if it comes apart totally. No way of telling when that will happen. During that year when mine was failing I took it out on 8 hour wheeling trips all over plus another 45 minutes of highway driving. Probably stupid but luckily nothing crazy happened.
That's what I'm doing Friday. Good thing its almost the end of wheeling season and I have a reliable car to drive in the winter.

I've got a friend with a rusty 98 UC Grand with only 107k, I might buy the whole jeep off him and swap rear axles assuming the gear ratios are the same. It would be cheaper than paying a specialty shop to reset the gears. Then I'd also have plenty of spare parts for the 1% of my jeep that isn't covered by AutoZone's warranty.
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Unread 12-10-2012, 05:04 PM   #10
PolkaPower
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Quote:
Originally Posted by ZJMatt View Post
That's what I'm doing Friday. Good thing its almost the end of wheeling season and I have a reliable car to drive in the winter.

I've got a friend with a rusty 98 UC Grand with only 107k, I might buy the whole jeep off him and swap rear axles assuming the gear ratios are the same. It would be cheaper than paying a specialty shop to reset the gears. Then I'd also have plenty of spare parts for the 1% of my jeep that isn't covered by AutoZone's warranty.
4.0 has 3.55 gears and the 5.2 has 3.73. There are some exceptions. I believe you could get the 3.73 gears on the 4.0 for extra if requested.
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Unread 12-12-2012, 02:00 PM   #11
Insane_Jeep
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i'm going to get my rear looked at soon, my 4.0 laredo has 3.73's in it (factor as i can tell), had one axle changed out, the driver side still looked fine, so next up is the bearings in the diff...then to take care of bushings all through out the suspension and shocks, right now i'm just trying to get mine back to stage 0...
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Unread 12-12-2012, 02:01 PM   #12
PolkaPower
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Originally Posted by Insane_Jeep View Post
i'm going to get my rear looked at soon,
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Unread 12-12-2012, 02:25 PM   #13
Insane_Jeep
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nah, seriously...just got my bonus from work, and thats the first thing on the list. this jeep means a lot to the family and we are wanting to keep it running nice and smooth, also before it frags and it cost a lot more
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