I recently replaced my U-Joints on my 70 chevelle SS. I forgot to mark the driveshaft before I removed it from the trans and differential now I have a vibration that begins around 60mph and gets worse with increased speed. I had to melt out the old plastic seals for the old u-joint caps, now I have u-joints that have a c-clip to hold them in. I was told to have the driveshaft re-balanced, will this correct the problem? is there any markings on the slip yoke or the trans so I can line it up correctly? PLEASE HELP!!!I am sure one of you good folks out there have done this task on your chevelles.

Have you tried removing it, turning it 180 degrees and reinstalling it?

do you mean turning the slip yoke on the trans end or the differential end 180 degrees. or the whole shaft?

Turn the whole shaft, remove from diff., pull out of tranny turn 180 degrees and reinstall.