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Old 09-15-2011, 09:47 AM   #1
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Default help diagnosing rear end vibration/thump

I suppose is should start by saying the relationship of the bump/thump/vibration (whatever i should call it) speeds and slows in direct proportion to the speed of the vehicle.

I picked up a half-shaft and hub assembly from Mazda heaven yesterday. But not sure it will help me at this point. Once I got home I jacked up the car, put it in drive and let the wheels spin while in the air. I noticed a light clinking or clicking sound coming from the right rear of the car, could this be a bad half-shaft?

I also can visibly see the wheel, bobbing up and down as it spins. I decided to mark the ‘high’ spot while it was spinning. After doing so, I removed the wheel, turned it 180 deg clockwise and remounted it. This way I figured if the hub/axle was bent, the new marking would be on directly opposite (top/bottom) of the tire. Well, while spinning I marked it again, and the marks were in the same spot as the first go around. This makes me think the tire is worn unevenly and ‘bent’, somehow.

Next I marked the relationship of the tire markings to the hub and proceeded to move the driver side rear tire (#2) to the passenger rear hub to check if and where it would ‘mark’ while spinning. This wheel/tire while spinning has a less severe rotation flaw. After checking the very small mark on tire #2 to the mark on the hub, I noticed that they do not line up, but are off by about 30 degrees.

After this test I checked the hub for any ‘play’ and found none.
Other than the clicking noise coming from the right rear, I cant see anything wrong with it.

Maybe it’s the tire itself. Maybe its more than that. getting stumped here.
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Old 09-15-2011, 10:39 AM   #2
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If its a and you cant figure it out i've got a 1.6 diff for sale as long as you live close to Kentucky.
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Old 09-15-2011, 09:49 PM   #3
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it's probably what's known as a "tread ply separation" it'll probably get worse and worse until a chunk of tread busts loose or the tire blows out. go to a good tire place like discount tire and they can verify it. i just had a tire do the same thing on my tow vehicle. replaced it, now 2 others are starting to do the same thing. it should be noted that i had a vibration that gradually got worse for a year before the blowout.
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Old 09-15-2011, 10:19 PM   #4
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Rear end vibration!? Remove the vibrator from your rear end!

Now that that is out of the way... it's not at all uncommon to have a tire our of round like this. Has the car sat for any long periods recently, without being moved? It may just be a flat spot on the tire, or it could be like spoolin said, something more serious with tire tread separation.

Does the tire itself seem out of round in relation to the center of the hub, or is it just the entire tire bouncing around, with a moving center of rotation, like its severely out of balance?
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Old 09-16-2011, 01:51 PM   #5
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took the tire back to discount tire yesterday. again, they confirmed the tire is within spec and the wheel is fine as well. they even did a rolling weight test to verify.

car is my DD, so no it doesn't sit. vibrations started after i popped a curb a few months back.

at this point i am going to begin the rear hub and half-shaft swap. argh.
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Old 09-20-2011, 06:33 PM   #6
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Rear hub swapped, problem solved! finally! old bearings were full of metal shavings and completely trashed.
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