09 Jun 11 16:14, Mike Luther wrote to All:

 ML> Thoughts please?

Looks like you've covered all the bases. I'd bet that the problem was
there all along, just covered up by the air bag system. Once you went to
springs, that just manifested it more.

 ML> Following that work, the vehicle level matched exactly the same at
 ML> rest as it had been with the air bags.

Not necessarily a good or bad thing. But could effect the driveshaft
angles at both ends of the shaft.

 ML> It was a little stiffer along the roadway, but seemed to be just
 ML> fine. However, now the 'driveshaft' vibration seemed to be stronger
 ML> and, as the next couple thousand miles rolled up, got MUCH worse.

Hmmm.

 ML> The complete tire balance and roundness as well as wheel roundness
 ML> was carefully checked at two different places.  Perfect,

Perfect as in within .005 run-out? Or more?

 ML> OK, this is an alumninum shaft vehicle.

Chevrolet had this problem with their early 4th gen (93 and up) Camaros
with steel driveshafts. They replaced those with an aluminum driveshaft,
although any rear end noise, such as gear howling, got even more
pronounced. Some of the 6 cyl cars got a double shaft with a carrier
bearing in the middle. This cured the vibration problem though.

 ML> got a tow truck.  They took the shaft out and lifted the front end,
 ML> then towed it down the highway up to at least 80MPH while riding in
 ML> it studying for vibration!  Absolutely no vibration at all.  Smooth
 ML> as silk ride.

Question. Has anyone ever checked the pinion angle with all four wheels on
the ground? Does the angle at the transmission end match the differential
end.

 ML> expected, there is no felt pinion irregulartity.  The only thing that
 ML> looks like it can be done next will be to yank the third member and
 ML> attempt to trace this to pinion problems, one way or another. And
 ML> there is no rear suspension angularity problems or damage.  Now I am
 ML> familiar with the very rare issue with a rear pinion bearing problem
 ML> which does not result in pinion seal issues.  But in that there is no
 ML> really noteable pinion rotation irregularity seen, even if this is a
 ML> rear pinion bearing crack or whatever problem, I wonder?

Before yanking the third member, check to see how true the driveshaft
turns at the yoke. Could be the yoke was machined slightly off center.

 ML> Hunt for Red October. He and I agree.  This has to be a reasonance
 ML> issue as well.  But that said, how can this be just a pinion bearing
 ML> or third member problem? What is going on here?  Where is the
 ML> reasonance and why?

Resonance and vibrations are caused by the centrifugal forces applied to
those things that rotate at high speeds. Especially those that are out of
balance or do not run concentric, will cause your problem. i.e. the ring
gear could have been machined off center where the external diameter is
running out enough to allow centrifugal forces to be applied to the part
that isn't concentric with the differential bearings. Although something
like this would show up when you towed the vehicle without the driveshaft
in place. I'd check the andle of the driveshaft ends and the runout of the
yoke on the differential and if that doesn't do it, I can't think of
anything else...

                R\%/itt


 ..."We will not tire, we will not falter, we will not fail." - GWB


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