RW> 09 Jun 11 16:14, Mike Luther wrote to All:   
      
   Thanks Gentleman Witt   
      
    ML> Thoughts please?   
      
    RW> Looks like you've covered all the bases. I'd bet that the problem was   
    RW> there all along, just covered up by the air bag system. Once you went to   
    RW> springs, that just manifested it more.   
      
   Somewhat yes perhaps.   
      
    RW> Not necessarily a good or bad thing. But could effect the driveshaft   
    RW> angles at both ends of the shaft.   
      
   In this case absolutely the same at rest level as the air bag system.  For all   
   practical purposes this makes the shaft angles at both ends of the shaft the   
   same as before.  One thing most don't know, I think, is that if the pinion   
   shaft and drive/transmission shaft planar alignment is perfect, per what I   
   have learned is that the U-Joints will wear out!  That is because if the   
   planar angle is perfect in alignment, the needle bearings will never rotate   
   and will stay in the same spot .. thus creating intents in the U-Joint crosses   
   and yokes!!   
      
    RW> Hmmm.   
      
   Yes ,,, Hmmmm   
      
    RW> Perfect as in within .005 run-out? Or more?   
      
   Well, you are correct as to what you propose.  However in this case, since the   
   vibration frequency absolutely is *NOT* at wheel revolution speed, this makes   
   the above wheel roundness and so on sort of not important.  Unless, it could   
   be a phase cancellation or amplification at some precise speed that is part of   
   the shaft speed.  And in this case the ring gear - pinion gear ratio would   
   have to be a precise 2 to 1 or 3 to 1 gambit I'd think. Which it is not.   
      
      
    ML> OK, this is an alumninum shaft vehicle.   
      
    RW> Chevrolet had this problem with their early 4th gen (93 and up) Camaros   
    RW> with steel driveshafts. They replaced those with an aluminum driveshaft,   
    RW> although any rear end noise, such as gear howling, got even more   
    RW> pronounced. Some of the 6 cyl cars got a double shaft with a carrier   
    RW> bearing in the middle. This cured the vibration problem though.   
      
   This is a very short single shaft vehicle . Less than 72 inches total   
   including the front yoke.   
      
    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.   
      
    RW> Question. Has anyone ever checked the pinion angle    
    RW> with all four wheels on   
    RW> the ground? Does the angle at the transmission end match the differential   
    RW> end.   
      
   No not perfectly.  But again, go back and read my post on that above.  I used   
   to think that same thing.  But I was taught by a very serious bearing   
   professional that it absolutely CANNOT be perfect because that ruins the   
   U-Joints!!   
      
    RW> Before yanking the third member, check to see how true the driveshaft   
    RW> turns at the yoke. Could be the yoke was machined slightly off center.   
      
   They did that at the transmission end.  We still have not, as best I can tell,   
   done that at the pinion end.  However, if it was actually a pinion error,   
   there would have been vibration there well back into the less than 40,000 mile   
   range.  And there was not.  The vehicle was perfectly quiet.   
      
      
    RW> Resonance and vibrations are caused by the centrifugal forces applied to   
    RW> those things that rotate at high speeds. Especially those that are out of   
    RW> balance or do not run concentric, will cause your problem. i.e. the ring   
    RW> gear could have been machined off center where the external diameter is   
    RW> running out enough to allow centrifugal forces to be applied to the part   
    RW> that isn't concentric with the differential bearings. Although something   
    RW> like this would show up when you towed the vehicle without the driveshaft   
    RW> in place. I'd check the andle of the driveshaft ends    
    RW> and the runout of the   
    RW> yoke on the differential and if that doesn't do it, I can't think of   
    RW> anything else...   
      
   I don't disagree with you at all here.  However in that the vibration is   
   absolutely only there at pinion speeds.  Plus, again as noted, this was not   
   there at all when the vehicle was towed with no shaft in it and checked.  Now,   
   the pinion vibration COULD have still been there.  And with that in mind,   
   without the driveshaft to FOCUS that ripple into place at whatever reasonance   
   is there to do this, frame/shaft or otherwise we wouldn't know, would we?  And   
   who gets to ride under the vehicle at 90MPH to touch the third member with a   
   finger to feel what?   
      
   Wince .   
      
   Mike Luther @ 1:117/100   
      
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