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Physicistkev

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2018 JLU Sport S. Rancho 3” lift with stock wheels and 35” tires along with 4.56 gearing. Adams front drive shaft and stock rear drive shaft. All installed at 20k miles and now has 50k miles. Isn't abused, but does go on blue trails a few times a year and I’ll venture over a black obstacle on occasion. Tows a small boat, around 3000#s, to and from the ramp (30 miles one way) and I did tow it from Northern Virginia to the Florida Keys and back in June.

The issue started about a week ago. Only after being warmed up. Happens quicker when towing or when driven harder.

Sounds like a chirp, or a kazoo (yeah it’s strange), that is not constant. My daughter says it sounds like a cricket. I’ve never heard a car make a noise like this. Think of a chirping fan belt, but more organic. Anywho…

It chirps in time with the rotation of the rear drive shaft and is coming from the rear half of the car. It happens at low speeds (15mph to 30mph) and it chirps under light acceleration. It chirps in 2wd, 4wd and 4w low. The speed is much slower in 4w low. Oh yeah, happens in reverse at the same speed. Pressing on the gas more, makes it go away. Turning and putting the car in neutral makes no difference. Braking or using the parking brake makes no difference. If I let off the gas, it continues to chirp until I reach a speed of about 15mph or less. However, when I take my foot of the accelerator, sometimes it’s intermittent as I slow down.

I’m thinking CV joints on the rear drive shaft or the rear differential. The differential seems unlikely as the chirp sounds “open”. Like it’s not inside something or muffled in any way. I would swear someone taped a harmonica with a way to make it oscillate under my car.

The differential doesn’t make any grinding, whirring, humming or any of the classic bearing failure sounds. I haven’t checked the fluid yet, but that will happen tomorrow. Searching for the forbidden glitter.

CV boots look perfect on the drive shaft. No leaks or fluid can be seen on the rear differential or drive shaft.

GoPros will get mounted after the rear differential fluid check and hopefully I can locate the sound with more fidelity.

Anyone have any suggestions I might be missing? Thanks in advance.
 
Ddays said:
It really sounds like you may have tweaked an axle flange. Try jacking it up and checking the runout of the rear discs to see it one is out.
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Nice. I hadn’t thought of that. I did have it up on my quick jack and did a tire rotation and checked all the rotors and pads visually, but didn’t check for anything being warped/bent.

I did run the car while it was up and there was no wobble and I couldn’t reproduce the issue, but this was before I figured out I had to warm up the transmission for it to happen.

I’ll check that out when I do the fluid check.

Thanks
 
Ddays said:
It really sounds like you may have tweaked an axle flange. Try jacking it up and checking the runout of the rear discs to see it one is out.
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^^^this. That would be my guess as well for sure. Though since you did mention some towing, if the flange is in fact ok, may want to also check rear axle shaft bearings. Low or even really bad diff fluid can damage them (diff fluid is what lubricators them). But I’m still willing to bet bent flange.
 
Disciple Off Road said:
^^^this. That would be my guess as well for sure. Though since you did mention some towing, if the flange is in fact ok, may want to also check rear axle shaft bearings. Low or even really bad diff fluid can damage them (diff fluid is what lubricators them). But I’m still willing to bet bent flange.
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Rear axle shaft bearings. These are the outboard bearings just behind the axle mounting plate, correct?
 
Disciple Off Road said:
Yes correct.
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Okay, thanks.

The plot thickens. I drained the diff and there was some lighter gray flows in the oil that drained, but nothing truly glittery. Also, when I cleaned the drain pan itself I could see two dozen little flakes. Nothing that I would say made me think there was a lot of wear or abnormal wear. The oil is 30k miles old and seemed normal to me. But…

I noticed that the driver side rear brake dust guard had a wet pattern that appeared to be a leak from the end of the axle tube. To me, that strongly supports an axle bearing and seal issue, which may or may not be because of a bent axle flange. I’ll check the run out later today.

Just thinking ahead here. What’s the cost to pull a bearing and press a new one on? Is it worth doing both sides since I have to do one? A stock axle is $250ish with a chromoly pair being $600ish. Depending on the cost to pull/push bearings then I’m thinking a new set of axles for an R and R may not be a bad option.

Thoughts?
 
Definitely confirm if it’s bent as that will narrow your options down quickly.

Replacing the axle shaft bearing and/or seals requires you remove all existing parts. This is what you will need, a Set 10 axle bearing kit.

IMG_1386.jpeg

These will sometimes run you around $85 for one side. Installing a new set will vary in labor depending on the shop.

Most people do opt for completely replacing with new chromolys for the upgrade, warranty and they come fully assembled.
 
Disciple Off Road said:
Definitely confirm if it’s bent as that will narrow your options down quickly.

Replacing the axle shaft bearing and/or seals requires you remove all existing parts. This is what you will need, a Set 10 axle bearing kit.

View attachment 430010

These will sometimes run you around $85 for one side. Installing a new set will vary in labor depending on the shop.

Most people do opt for completely replacing with new chromolys for the upgrade, warranty and they come fully assembled.
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Yeah. In the hour I’ve been looking this morning, I can get a Dana 44 Advantek chromoly for open/trak-loc (which should be the one for my factory LSD) or a set of Revolution non-Rubicon 4340 Discovery series for a bit more.

With labor costs locally ($100-$150 an hour), I’m very inclined to just buy the new axles. The remove and replace seems very easy, with breaking the axle free and removing the old race being the most difficult things. The race removal shouldn’t need a tool, just working it back and forth should do the trick.

I’m still going to look at the axle plate, because I want to find the cause of the accelerated wear. I would hate to replace everything and then the problem to come back if it’s not from a bent axle plate.

I’ll report back here so that anyone that has a similar issue can at least have some confidence to pursue this as a potential cause.
 
Physicistkev said:
Yeah. In the hour I’ve been looking this morning, I can get a Dana 44 Advantek chromoly for open/trak-loc (which should be the one for my factory LSD) or a set of Revolution non-Rubicon 4340 Discovery series for a bit more.

With labor costs locally ($100-$150 an hour), I’m very inclined to just buy the new axles. The remove and replace seems very easy, with breaking the axle free and removing the old race being the most difficult things. The race removal shouldn’t need a tool, just working it back and forth should do the trick.

I’m still going to look at the axle plate, because I want to find the cause of the accelerated wear. I would hate to replace everything and then the problem to come back if it’s not from a bent axle plate.

I’ll report back here so that anyone that has a similar issue can at least have some confidence to pursue this as a potential cause.
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You want to check the flange with it still installed on the Jeep so you can rotate it to check the runout. In some cases if really bad, you will visually see the bend/movement while rotating.

Yes removal is easy, remove 2 18mm caliper bolts, 4 18mm axle retainer nuts and to be safe, 8mm abs sensor bolt to pull out of the way. The race should walk out fairly easy but a crows foot tool can help.

These are the axle shafts you will need if you elect to replace them completely;

Revolution JL Non-Rubicon 4340 Chromoly Axle Kit
(make sure you don't have a dana35/M200 rear axle)
 
Okay. First thing. The rear disk was VERY stubborn. However, once it was removed I hooked up the old trusty dial, that I picked up this afternoon, and have found that the rear driver side plate is .007 (seven thousandths) out for a full rotation on the face.

I have to be honest. I don’t know if that’s good or bad. Seven thousandths seems like a small amount, but I can’t find a tolerance reference for this.

image.jpg
Including shot of the setup so anyone can point out anything I’m doing wrong. I am certainly not above laughing at myself for doing it wrong.

To rotate the plate I turned the opposite wheel as I found spinning this side created several thousandths of variance. As a side note, the driver side axle has .011 (eleven thousandths) of play in and out. Again, I have no idea if that’s good or bad.

I’m going to remove the passenger side tomorrow and measure the runout to see if it’s the same.
 
And now I know that there is vertical runout and lateral runout. What I measured above is lateral runout. For vertical runout I need a “teeter totter” attachment for my dial because you have to measure the outer circumference of the axle hub. The protrusion that centers the brake disk on the hub. The wheel studs get in the way of measuring this with just a dial.

I have also found that the lateral runout shouldn’t be more than .003 (three thousandths). If that’s correct, than my .007 is more than double the tolerance.
 
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