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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