Unsolved mystery: "chu-chu-chu" sound and strange rotor wear

toximus

toximus

I live in my Jeep
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Halloween is right around the corner and I have an unsolved mystery for you guys. Any guesses as to what the issue is or how to fix it?

Last week @Mrs Tox 's Rubi TJ (khaki TJ in sig) got processed with a new sound while in stop and ghoul traffic in Chicago. The dull scraping "chu-chu-chu" sound seems to be coming from the rear right tire area.

Fact 1: The Jeep has a little gear oil leaking from the pinion seal. No other gear oil is leaking.
Fact 2: The brakes can be touched and aren't overly hot.
Fact 3: The sound mostly occurs under acceleration between 2-35mph.

Anyone know what the issue is? I have a theory.
 
Taking the wheel off I found that the front parking brake pad has been rubbing on a particular section of the rotor.

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20211021_132454.jpg
 
I also checked the diff fluid level. It wasn't as full as I had left it 2 years ago, but still had what seems like plenty of fluid. It was on my list of fluids to change anyway so I drain and filled. Nothing abnormal with the fluid and probably would have been fine for another 20k+ miles.
 
B00mb00m said:
Stuck caliper pin.
Click to expand...

The calipers slide smoothly. The only oddity there is the inner brake pad is worn at a slight angle and isn't wearing quite as nice as the outer pad. But 10k+ miles remaining on the pads (I need to order some so I have them ready).
 
toximus said:
The calipers slide smoothly. The only oddity there is the inner brake pad is worn at a slight angle and isn't wearing quite as nice as the outer pad. But 10k+ miles remaining on the pads (I need to order some so I have them ready).
Click to expand...
warped rotor?
 
While I had it apart, I made sure everything moved smoothly and quietly. I washed everything thoroughly with a small brush and hose.

I can't imagine the rotor hat (where the parking brake rides) getting out of round after being fine for longer than I've owned the Jeep.

My theory is that the axle shaft bearing that presses on is starting to wear which is allowing the end (and thus the rotor) to spin out of round when accelerating as the tire "rides up". When the tire is spinning above 35mph the sound goes away which I suspect is because the tire is balancing causing the shaft to spin more true within the bearing.
 
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toximus said:
Yup.
Click to expand...
I had a similar sound coming from mine...I surmised it to be the parking brake too. The next day, after 250 miles of highway driving and 5'ish hours of trail riding...my wheel fell off at the spacer/adapter. At that time, I changed my theory to the wheel adapter was slightly loose and the tire was moving, ever so slightly, making a noise...or the tire was flexing the brake disc a little, causing the contact with the parking pads.

I'd be willing to bet you put it back together and don't hear a thing.
 
Mike_H said:
I had a similar sound coming from mine...I surmised it to be the parking brake too. The next day, after 250 miles of highway driving and 5'ish hours of trail riding...my wheel fell off at the spacer/adapter. At that time, I changed my theory to the wheel adapter was slightly loose and the tire was moving, ever so slightly, making a noise...or the tire was flexing the brake disc a little, causing the contact with the parking pads.

I'd be willing to bet you put it back together and don't hear a thing.
Click to expand...

Since the noise started, we've driven the Jeep another 1000 miles.

It's back together again and still making the same noise on the test drive. Thankfully I didn't see any indication that the spacer has been moving. I also check the spacers every oil change or so and never have seen them loosen up.
 
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toximus said:
Since the noise started, we've driven the Jeep another 1000 miles.

It's back together again and still making the same noise on the test drive. Thankfully I didn't see any indication that the spacer has been moving. I also check the spacers every oil change or so and never have seen them loosen up.
Click to expand...
Glad it's not that then. Having a wheel fall off is an unsettling experience.

I guess my noise wasn't a cho-cho sound either. More of the dry scraping sound you hear when a u joint runs dry. In fact, my first thought was the drive shaft...
 
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