Turbine D
I get from Wojtek that he is offering a "Fluid Drive" argument against torque problems that may result in stress wear or fracture. I'm not sure it obtains to this discussion, however, at the cusp of Torque "reversal", there is enormous stress on the rigid coupling, having to translate gobs of torque from components that were at one moment driving in one direction, but quickly changing to "driven" mode. Vibration could mimic this reversal of torque, but in more and shallower "events". Load, Unload, Load, etc. A resonant frequency would cause the same, but even more chaotically. At the "Null" point, where torque is balanced (neutral) any wear or excess tolerance in these bearings would cause chaotic vibration in erratic "Ovoids", a chattering mess of blurred steel balls, raceway and cage. Can you hear the din of bearings "floating" as the result of intense and unplanned for motion?? We've all heard it. Rattle, shriek, and stop.