[rotorwrench]

As was already mentioned, the small diameter and the fact that is is solid have a lot to do with whether an imbalance will affect it. The whipping of a solid shaft can be a problem so Ford used a damper like most drive systems with long shafting. A larger tubular shaft has no mass on it's center line due to being hollow and many are welded tube so they are very much affected. Whipping is generally not a problem on shorter hollow tube shafts but longer ones need the added stability under large torque loads. A lot depends on diameter and length.