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Discussion Starter #1
I bought a half shaft from Auto Zone. I noticed the shaft is missing one part the OEM shaft had. It "appears" to be a useless piece of rubber in the middle of the shaft. Anyway, I installed the aftermarket shaft even with the difference.

Note the part circled in Red is what I am referring to.

[attachment=20656:cv_front...le_shaft.jpg]

Now, no matter what gear, when I hit about 3-4K on the tachometer, I can hear a noise that seems to "travel" from the center of the car to the outside wheel. My theory, and feel free to correct me if I am wrong, is that rubber piece balances, shifts, or eliminates a frequency resonance in the shaft, maintaining a quiet ride.

Any thoughts?

(By the way this website has been a life saver so far!)

Thanks All!
 

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your right, it would seem that the shaft is out of balance. hopefully autozone will change it for you
 

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Discussion Starter #3
What sort of proof can I give them that says
1) The shaft is out of Balance
2) The rubber piece noted above is not optional
3) The shaft is faulty in some other way

?

Does any one know of any "official" website or document that states any of this?

Thanks!
 

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Discussion Starter #4
OK, I've been trying to figure this out and so far I am positive, it is NOT a balance issue. From what I've heard from many is that if it was simply balance, it would vibrate at almost all speeds and torques.

So, what I have discovered is that seemingly "useless piece of rubber" has a significant purpose.

Think of the shaft like a guitar string. In many respects it's hard to think of a solid steal shaft flexing like a guitar string, but in reality, this is exactly what it is doing. At different RPM's, torques, etc. the engine sends out all sorts of frequencies, almost like a speaker and almost everything has a "natural frequency" (a frequency at which the object naturally vibrates once it has been set into motion) where it goes into resonance.

In this case with the drive shaft, the engine running at 3-4K is putting out a frequency which is causing the shaft to resonate, turning the shaft into nothing more than a heavy duty guitar string. Ok, so why does that matter other than it being noisy? When a object is "resonating" at it's natural frequency it is also flexing, heating up, stressing and will eventually fail. Most have us have bent some sort of metal back and forth until it hardened the material and broke. The same thing can happen here. In all honesty, I doubt the solid shaft itself breaks... more than likely what all that will cause is it will also be vibrating the dog snot of of neighboring components and will reduce their lifetime. The CV joints, wheel bearings, etc will probably fail first.

So in turn, Hyundai's engineers must have known this... that is why this "useless" piece of rubber is there. The rubber disperses the frequency and eliminates this issue.

This could be a serious issue for others running without that piece.

I guess not of this would bother so much if it hit this frequency at lets say 6-7K RPM. But, it hits it at a horrible point. I do a lot of highway driving. And right about 70 MPH (+/- 3 MPH) the engine is turning near that 3-4K mark and guess what I hear? Yeah, the dumb thing resonating. Guess what the speed limit is in Indiana... 70 MPH! You can even hear it vibration in stereo. At 69 MPH, it sounds like its in the center of the car at 73 MPH it sounds like it on the right side of the car.

(If you are bored, this is the simplest, i have seen "natural frequencies" explained. http://www.cs.wright.edu/~jslater/SDTCOutr..._frequency.htm)

I'm kind of ticked about this. Yeah at this point the nuts are still lose and "you get what you pay for" but aftermarket or remanufactured parts are promised to "Meet or exceed OEM's requirements."

... RIGHT! ;)
 

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Discussion Starter #6
Well Auto Zone has been going way above the "come get another and put it on yourself" attitude I expected. They thought it was a shaft that was out of balance as well and I actually have another half shaft on the car now. This half shaft is also missing the damper. I get the exact same result with this one. (A loud noise at 3,000 RPM no matter what gear).
 
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