13 Jun 11 10:01, Mike Luther wrote to Roy Witt:   
      
    RW>> Not necessarily a good or bad thing. But could effect the driveshaft   
    RW>> angles at both ends of the shaft.   
      
    ML> In this case absolutely the same at rest level as the air bag system.   
      
   Which isn't good or bad, unless the angles have changed to make things   
   worse.   
      
    ML> For all practical purposes this makes the shaft angles at both ends   
    ML> of the shaft the same as before.  One thing most don't know, I think,   
    ML> is that if the pinion shaft and drive/transmission shaft planar   
    ML> alignment is perfect, per what I have learned is that the U-Joints   
    ML> will wear out!   
      
   Just the opposite of what most driveline people say.   
      
    ML> That is because if the planar angle is perfect in alignment, the   
    ML> needle bearings will never rotate and will stay in the same spot ..   
    ML> thus creating intents in the U-Joint crosses and yokes!!   
      
   I think that this would be true, if the driveshaft were straight from the   
   trans to the differential. Since the shaft isn't straight but at an angle   
   to each other, the needle bearings will rotate, actually, oscillate back   
   and forth in the cup as the pitch of the angle changes the position of the   
   bearing shafts.   
      
    RW>> Perfect as in within .005 run-out? Or more?   
      
    ML> Well, you are correct as to what you propose.   
      
   My thinking before reading the tow truck test. Which no longer applied   
   after I read it.   
      
    ML> However in this case, since the vibration frequency absolutely is   
    ML> *NOT* at wheel revolution speed, this makes the above wheel roundness   
    ML> and so on sort of not important.   
      
   Since they've been proven (tow truck) to be good enough to eliminate them   
   from the problem.   
      
    ML> Unless, it could be a phase cancellation or amplification at some   
    ML> precise speed that is part of the shaft speed.  And in this case the   
    ML> ring gear - pinion gear ratio would have to be a precise 2 to 1 or 3   
    ML> to 1 gambit I'd think. Which it is not.   
      
   3.42:1 most likely.   
      
    ML>> OK, this is an alumninum shaft vehicle.   
      
    RW>> Chevrolet had this problem with their early 4th gen (93 and up)   
    RW>> Camaros with steel driveshafts. They replaced those with an aluminum   
    RW>> driveshaft, although any rear end noise, such as gear howling, got   
    RW>> even more pronounced. Some of the 6 cyl cars got a double shaft with   
    RW>> a carrier bearing in the middle. This cured the vibration problem   
    RW>> though.   
      
    ML> This is a very short single shaft vehicle . Less than 72 inches total   
    ML> including the front yoke.   
      
   As is the Camaro. The difference in rear suspension is the torque arm   
   between the differential and transmission. Both cars are 4 link coil   
   spring suspensions, perhaps the Buick only has 3 links. Plus the Camaro   
   has a cross link, sometimes referred to as a panhard bar/rod.   
      
    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   
    RW>> differential end.   
      
    ML> No not perfectly.  But again, go back and read my post on that above.   
      
   I think this is where I would do some further investigation. Both angles   
   should be as near to each other as possible, with the differential yoke   
   pointing down, not up. Under torque it will tend to rise anyway.   
      
    ML> I used to think that same thing.  But I was taught by a very serious   
    ML> bearing professional that it absolutely CANNOT be perfect because   
    ML> that ruins the U-Joints!!   
      
   Suit yourself.   
      
    RW>> Before yanking the third member, check to see how true the   
    RW>> driveshaft turns at the yoke. Could be the yoke was machined   
    RW>> slightly off center.   
      
    ML> They did that at the transmission end.   
      
   The transmission's yoke could have been splined off center. Not very   
   likely, but not impossible.   
      
    ML> We still have not, as best I can tell, done that at the pinion end.   
      
   A bit harder to do.   
      
    ML> However, if it was actually a pinion error, there would have been   
    ML> vibration there well back into the less than 40,000 mile range.  And   
    ML> there was not.  The vehicle was perfectly quiet.   
      
    RW>> Resonance and vibrations are caused by the centrifugal forces   
    RW>> applied to those things that rotate at high speeds. Especially those   
    RW>> that are out of balance or do not run concentric, will cause your   
    RW>> problem. i.e. the ring gear could have been machined off center   
    RW>> where the external diameter is running out enough to allow   
    RW>> centrifugal forces to be applied to the part that isn't concentric   
    RW>> with the differential bearings. Although something like this would   
    RW>> show up when you towed the vehicle without the driveshaft in place.   
    RW>> I'd check the andle of the driveshaft ends 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...   
      
    ML> I don't disagree with you at all here.  However in that the vibration   
    ML> is absolutely only there at pinion speeds.  Plus, again as noted,   
    ML> this was not there at all when the vehicle was towed with no shaft in   
    ML> it and checked. Now, the pinion vibration COULD have still been   
    ML> there.   
      
   Thus proving that the pinion angle isn't correct. It wouldn't vibrate   
   without a shaft in it, at least not noticably. When you put the shaft back   
   in, it vibrates.   
      
    ML> And with that in mind, without the driveshaft to FOCUS that   
    ML> ripple into place at whatever reasonance is there to do this,   
    ML> frame/shaft or otherwise we wouldn't know, would we?  And who gets to   
    ML> ride under the vehicle at 90MPH to touch the third member with a   
    ML> finger to feel what?   
      
   I knew a cat that did that once. He ruined a perfectly good driveshaft.   
      
    ML> Wince .   
      
                   R\%/itt   
      
      
    ..."We will not tire, we will not falter, we will not fail." - GWB   
      
      
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