Loud driveline growling (bearing?) noise - need help please!

Looking for advice about my worsening growling noise (sounds like a bearing) please and thank you...

99 XJ classic, 172K miles, 4.0, AW4, 231 TC, 8.25 rear, 3.5" RE Super Flex, 1" TC drop, 2* axle shim, 31" BF TKO2.

While driving I am experiencing a worsening growling noise, that gets especially bad faster than about 40mph. It is especially bad sounding when on jack stands. I believe I have somewhat systematically diagnosed it, but am stuck now. Here is what I have done so far:

With front wheels on the ground, and no ft driveshaft, rear tires removed and rear axle on jack stands and in 2WD, the sound was especially bad in the garage over 35 mph, could feel the growling in the rear end. I installed a (seemingly) good 8.25 rear axle from a JY donor, no noise change.

I installed new Moog U joints in rear driveshaft, no noise change.

The T-case fluid was black, so I installed a (seemingly) good 231 T case from a JY donor, no noise change.

I put rear wheels on the ground, removed rear driveshaft, put front axle on jack stands and ran it in 4 High, noise still prevalent.

Am I correct in thinking that this leaves the transmission as being the culprit? Maybe output shaft bearing? The tranny shifts fine, fluid is not low, and is kinda dark but doesn't smell too burnt or anything. Am I missing something, or should I take it to a tranny shop? Thanks much!

Does the noise go away in park making it not the engine or flex plate?

What does it do in Neutral at say 2000 to 3000 rpm?

Have you tried 1-2 manual gear to see if it is only a noise in say 3rd or OD gear?

Have you tried removing both axle shafts to make sure both axle shafts are not bent or ?????

Sounds like you are close to the answer for sure.

Ecomike, thanks for the reply.

No noise in park, or in neutral.

Can definitely still hear it in 3, and pretty sure in 2/1, although tougher to get to 35/40mph to test as engine revs were getting kinda high.

Also no noise in drive with both driveshafts removed, for what that's worth.

I haven't removed axle shafts, but is my logic correct in thinking that it cant be axles or wheel bearings as the noise is prevalent and the same with each axle isolated by having front or rear wheels on the ground during my testing?

A mechanics stethoscope really doesn't cost that much. I've narrowed down a sound to within one or two connecting rod bearings. And I'm half deaf.

Sound travels in the drive train. It can really fool you no matter how good you are.

Interesting:

"Also no noise in drive with both driveshafts removed, for what that's worth."

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That is worth a lot!!!!! That says to me it is not the transmission!!!party1:

That might leave the transfer case but you swapped it out so not likely to be it either.

"I haven't removed axle shafts, but is my logic correct in thinking that it cant be axles or wheel bearings as the noise is prevalent and the same with each axle isolated by having front or rear wheels on the ground during my testing?"

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It is possible the noise has two sources. Say it went through water that was left in all four front and rear bearings or U-joints.....

You could have an axle shop spin balance the drive shafts to make sure they are not both out of balance or bent. That can be a problem. But the drive shafts would be a vibration, and usually a growl as well from bad U-joints, but you replaced the u-joints leaving just vibration, so less likely to be driveshafts since you said it was a growl?

This is a lifted rig right? Could they be in a bind from an incomplete lift job, or have you had this as a working rig that suddenly developed this issue? I am not a lift expert either, so not sure a lift bind would cause your problem. I think it is more of a low speed over bumps and turns issue. But with the jeep lifted and the free turning axle loose and at Max extension height that might adding to a bind issue????

That leaves axles and wheel/axle shaft bearings, but you said you replaced an entire rear axle assy right?

I am stumped at this point.

8Mud said:

A mechanics stethoscope really doesn't cost that much. I've narrowed down a sound to within one or two connecting rod bearings. And I'm half deaf.

Sound travels in the drive train. It can really fool you no matter how good you are.

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Say what??? LOL....

This is an odd one, no doubt.

Thanks for the replies and suggestions!

I have replaced both rear DS U joints and the T case side u joint of the ft DS, no noise change, and its definitely a growl, not vibe. Both drive shafts seem to spin evenly, and R & R w/o any strain. I dont think it could be both axles since there was no noise change after replacing the entire rear axle (drum to drum), and I have to think that it can't be in the front at all if the noise is still prevalent with the ft wheels on the ground in 2wd and no ft DS installed.

I dont think it could be the T case, as there was also no noise change after swapping it.

So if its quiet w/ no DS's installed, it can't be the tranny? That would be awesome! When I had the rear wheels and ft driveshaft removed and had the (new) rear axle on stands, as soon as I put the rear DS back in, the noise was back. I figured it was load dependent - but there really isn't that much load on it with no wheels and on jackstands, right?

I think the noise has been there for a while, but worsening now, and more noticeable as I have been correcting my other noises and vibes. The noise sounds really bad on stands and on the highway.

8Mud said:

A mechanics stethoscope really doesn't cost that much. I've narrowed down a sound to within one or two connecting rod bearings. And I'm half deaf.



Sound travels in the drive train. It can really fool you no matter how good you are.

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Ain't that the truth!
I hate trying to find these kind of noises, just replaced the spindle hubs on a sienna, everyone swore the sound was on the drivers side, when I pulled it the drivers was ok, passengers on the other hand was done for.
Even tires can cause bearing sounds. A friend of ours had a car that sounded like the rear bearings were about to let go, new set of tires and the sound was gone.

On this it sounds like everything is being systematically eliminated.
I'd drain the fluid and drop the pan on the transmission just to take a look and replace the filter while there (if the transmission looks decent no point in throwing a good filter in a bad transmission)
At this point I try to listen to the transmission as it turns, if it's the culprit I'd get a cheap used one, a transmission shop unless you can find a real honest one is going to charge a arm and a leg to rebuild.

Could torque converters cause a noise like this? Never had one go bad so I've go no idea.


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Pull the fuse to the AW4 computer and see if the noise goes away. Shift manually. That will test the torque converter lock up for noise at about 35-40 mph where it typically engages.

Starting to wonder if the small load, but high speed is making clutch plates slip or something in the AW4 slip/grind, but we are grasping at straws now.

Exhaust pipe rubbing/hum???

I really am stumped. And at that point it usually means something on the "it ain't that list" is the real problem still.

Edit: what about the manual fan on the front of the engine? Rubbing on the fan cowl or radiator when the engine is loaded, do to bad mounts?

How are the tranny and engine mounts?

After reading all of the posts, you said that noise is there with either driveshaft in and when both are removed, no sound. It's got to be something in the driveshafts. You are right at the limit at 3.5". Some people experience noise/vibes and some don't. At 40 mph, the driveshafts are spinning pretty damn fast and it could sound like a growl. You might want to check the pinion angles on both front and rear axles. You can shim the rear and the fronts have adjustments. The pinion needs to point directly at the transfercase output, maybe 1 to 2 degrees less in rear to account for spring wrap under power. In a worse case scenario, you might have to do the SYE and new driveshaft. Might be this.

Damn it, I missed the part in the OP about the transfer case drop and 2 degree shims. I still think it's in there somewhere. With full weight on rear axle, tranny in neutral , disconnect rear driveshaft at axle pinion and check to see if there is any binding, it should be able to drop lower than the pinion while turning the driveshaft.

I'm thinking at this point possible SYE for rear and adjust pinion angle for front.

Warlock1 said:

After reading all of the posts, you said that noise is there with either driveshaft in and when both are removed, no sound. It's got to be something in the driveshafts. You are right at the limit at 3.5". Some people experience noise/vibes and some don't. At 40 mph, the driveshafts are spinning pretty damn fast and it could sound like a growl. You might want to check the pinion angles on both front and rear axles. You can shim the rear and the fronts have adjustments. The pinion needs to point directly at the transfercase output, maybe 1 to 2 degrees less in rear to account for spring wrap under power. In a worse case scenario, you might have to do the SYE and new driveshaft. Might be this.

Damn it, I missed the part in the OP about the transfer case drop and 2 degree shims. I still think it's in there somewhere. With full weight on rear axle, tranny in neutral , disconnect rear driveshaft at axle pinion and check to see if there is any binding, it should be able to drop lower than the pinion while turning the driveshaft.

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I'll vote this option at this point too. I mentioned it earlier, but not as well explained as your post.

I thought the drive shafts were eliminated and the noise was still there?


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Ecomike said:

I'll vote this option at this point too. I mentioned it earlier, but not as well explained as your post.

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And I'll agree with you that the spin balancing and checking for slightly bent driveshafts would be part of the diagnostics also. Doesn't take much to come over a rock or something and dink a driveshaft and knock it out of whack.

Green Mesa XJ said:

I thought the drive shafts were eliminated and the noise was still there?


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No, check post #3

Warlock1 said:

No, check post #3

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Oh, I missed that. Saw the first post where he pulls one then the other with the sound still there


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Haha, that's ok, I missed part of the 1st post. Sleep deprivation, lol.

Rear wheel bearings make a growl / roar. Youtube it.

That's true but OP hears it with either front or rear driveshaft connected. Could be multiple problems, possibly. Best to put your ear or stethoscope to the parts and don't be in denial. Lots of 8.25's have pinion problems. Carrier bearings make noise at any/all speeds over 20 generally, and wheel bearings can growl/roar too.