Well I'm back again. Told you I would be didn't I.
I need the advice of the greatest collection of minds to ever be assembled in one place again.
I have been riding the old 77 for about a week now and loving it. Have put several miles on it this week and have been noticing a funky vibration in the back end when the bike is at what I call the floating zone(not accelerating or decelerating)you know when there is really no torque either way.
It seems to happen at all speed ranges but is worse the faster the speed. also it seems to be worse when I am riding alone. If the wife is on with me it doesn't seem as bad. It could be I don't ride as fast with her on. I can take up the slack orback on offand it stops immediately.
So do I have a tire out of balance or something in the drive line that I should be really concerned about?
The Ujoint and & the splines on the drive shaft have excessive clearances and they vibrate just like you have described, some have learned to keep the driveshaft "loaded", by slowing more or keeping some power on, to kkeep the drive shaft from "floating" in the no torque zone, Or you can fix it.