ive chased a drivetrain issue for years.starts at 40 mph with a harmonic pulsating vibration and the faster you go the worse it got.i though i had it fixed a few times,but always came back.i tried several times with tire balance,new tailshaft bushing,new driveshaft from mancinni,re balanced by local shop,3rd member gone through.pinion angle at every possible angle,no change.i was ready to buy a new shaft from supershaft here on fabo ,but i found a 40 year old shaft in my parts tucked away in the corner of my garage,put it in for ***** and giggles.quess what, smooth.so anyone that has a simular issue,just because you buy a new driveshaft,dont mean its right.it pissed me off after all these years chasing this for it to be this.40 year old factory shaft as smooth as glass.