[tdangle]

1970 C20 with HD leaf spring suspension and full floater D60 4.10 gears. I have a vibration that comes in at aprox 50 strong at 60-65 and fading at 70mph. Also causing a loud rumble type noise in the cab.

Putting the truck on jack stands I can duplicate the issue. Items eliminated are wheels, brake drums and driveshaft/u-joints. I can remove the wheels and drums with no change. Entire 2 piece driveshaft has been rebuilt balanced and then later shortened (trans change) and rebalanced again.

Rearend shop said my pinion angle was off, so I installed 2 degree shims, shimmed the center carrier support lower. Working angles of the 3 u-joints are all under 2 degrees. Nothing has changed after all this work

I don't notice any noise but the vibration is strong, shakes the rear view mirror.

Any experts out there have comments?