[Shotimes] Vibration or picky...again ...Here comes the book! Part 1

[krazgeo@comcast.net]

Even using the Comcast website rather than my mailer, long messages won't get to the list....that's maddening.....maybe not to you!!  ;-)

First half......

On Mon, 07 Feb 2005 19:53:37 -0500, cmichaelo@optonline.net wrote:

>Vibration can be felt throughout the car, but especially in the dashboard.
>
>You can just visually see the dashboard vibrating.
>
>This vibration happens with all of my wheel combos (two 235/45-17 and one 235/40-18), but is somewhat more pronounced with the 40 seris tires.
>
>All wheels are balanced. Rims are "true" both radially and laterally. 
>
>The vibration is felt in one (sometimes two) particular mph "spots".  You go 3mph faster or slower and then there's no vibration.  So it's a resonance thingy.

Two possibilities.....actually one "pretty much this is it", and one possibility....

First....the fact that the dash is what is shaking points to the front wheels....99%
reliability.

Second...if you have to spin up the tire to balance it on the car, you WILL NOT HURT
the differential or transmission, as long as you start and stop gently, and do a
mnimum of shifting....for high speed balancing, start in 4th and shift to 5th after
the wheel is rotating at 15 to 25 mph indicated.....the speedo is half the speed of
the tire when one tire is stopped.  After your spin is done, let the tire slow down
in neutral, and use the brake after it is below 20 or so mph indicated.

Third.....after writing this and thinking about what you said, there is the
possibility that you have both problems, since the vibration migrates when you move
the wheel around on the hub.  There may be a very small imbalance on the hub/rotor,
plus you may also have a bit of an off center problem with your wheel(s).

Possibility....

A front wheel is a tiny bit off center as compared with the hub.  This problem
doesn't occur too often with newer wheels, but after they have a few hundred
thousand on them, like mine do, I have to center the wheel to the hub every time I
replace it after servicing something.  A 16th of an inch off center will result in
the equivalent of about an ounce and a half's worth of vibration at speed.   New
wheels _can_ be drilled incorrectly, but it doesn't happen often.  If one is drilled
wrong, you can live with it, employing the fix, or replace the wheel under warranty.
 Mine were re-drilled and re-tapered after I had inadvertently eaten the tapers out
by using standard SLO lugnuts, not realizing they were too small.  They were
redrilled incorrectly.  Since the car is where it is in its lifespan, I live with
it.

To check for out of roundness, jack up the corner of the car you want to check.  Put
the transmission in reverse, and let the engine idle in gear with the tire rotating,
and go over and look at the wheel's edge (tread).  Eyeball along the edge of the
tread looking at something fixed inside the wheelwell.  The edge of the tread should
not move back and forth as the tire rotates.  You'll need to go out and warm the
tires up before doing this test....they develop a flat spot when the car sits
overnight, which will give you a false indication.  I also have Pilot Sports, and
they are true enough in their construction to not induce an error in the reading. 
Mark the high spot, if you find one, with a tire crayon, and then back off a bit,
and with the tire continuing to rotate, compare the high spot on the tire with the
rim.  You should be able to see the high spot (max radius) in the rim at the same
spot as the crayon mark.

Part 2 to follow....