Whine in rear end

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890
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El Oeste
2001 Jeep Cherokee; 126K miles. I'm hearing a sort of whine or whirr that's coming from the back end of the Jeep when it's under power. As soon as I let off the accelerator, it's gone. It's a very low level but I can definitely hear it. I notoiced it right after I swapped out the rear diff. fluid last month. (Sucked out 2 qts. of dino 75W-90 and replaced with Syntec 75W-90.) But I'm not sure that has anything to do with it. I was listening more intently than I have before when I heard it. It may have always been there. The other thing worth mentioning is that my mechanic did some work on the axle a couple years ago because he heard a noise back there. A bearing I believe. I didn't get a chance to hear that noise so I can't compare. I'd appreciate any expert opinions. Thanks.
 

HawkeyeScott

Thread starter
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890
Location
El Oeste
I don't know which rear end it has. If it is one of those two bearings, how much time to I have? Will it get louder? It could be a few weeks before I can get it into the shop.
 

PT1

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5,746
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near the mistake
Is that diff spec an 80w90? If so go back to 80w90. If not it is most likely a bearing. But did you check the fluid level after you drove the vehicle? Try that first.
 
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4,434
Location
Massachusetts
 Originally Posted By: HawkeyeScott
I don't know which rear end it has. If it is one of those two bearings, how much time to I have? Will it get louder? It could be a few weeks before I can get it into the shop.
If it has ABS, then you have a Dana 35. The Chrysler 8.25 only came in non-ABS XJ's and is a slightly bigger/stronger diff. I'd be willing to bet you have the Dana 35, in which case, a good shop could change bearings fairly easily. If it's the carrier bearings, the shims are external. They would swap the bearings and then check backlash. If it's the pinion, it's still not too bad a fix. I don't know how mechanically inclined you are, but those axles are VERY cheap used and are very easy to swap out. That could be an alternative to going to a shop. Also, if you are barely hearing it, then I think you'd be fine for a couple of weeks. Just take it easy on the skinny pedal. I've driven some pretty broken (we call it Borken - LOL) stuff home from the trail and made it.
 
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2,439
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snowblind in TX
The problem is, the longer you let it go, the more chance there is you will trash a ring&pinion. Most times you have bearing material from the rollers and races getting ground into gear faces, as well as the pinion wobble due to uneven roller wear. Even after all bearings are replaced, and pinion depth and backlash are correct, you still have a noisy gearset. If you plan on all new internals, drive it till it drops.
 

HawkeyeScott

Thread starter
Messages
890
Location
El Oeste
I will check the oil level but I sucked 2 qts. out and put 2 qts. back in. The level should be the same as it was. I will indeed go easy on the skinny one. And I appreciate the junk yard suggestion. I have done that before and had good luck. Any idea why this would have happened? Thanks guys. You're a good resource and I appreciate the help.
 
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