Quote:
Originally Posted by Dynomite
Hi:
You rotated the drive shaft .......20% of issue went away.
You balanced tires.....50% issue went away (total 70%).
You thought about it.......another 20% of the issue went away 
I do not understand how the drive shaft balance (20% of problem) and tire balance (50% of problem) would not be rpm dependent (in gear at 75 mph or lower speeds in same gear).
I do not understand how depressing the clutch while at 75 mph would reduce the vibration if in fact you depressed the clutch at 75mph and let the engine idle as you were coasting at 75 mph.
I assume (the sp just for you  ) the circumstances are not as I envisioned from your explanation  |
Depressing the clutch while at 75mph, would reduce a driveshaft vibration, because it's unloading the driveshaft from the transmission end. Yes, it's still spinning, but it's unloaded, basically.
Depressing the clutch would have no impact on vibration due to poor wheel balance, because the forces that induce vibration in the wheels would not be changed, as I understand it. I'm no physicist or engineer, though.