[rotorwrench]

The solid shafts become more unstable to torsional forces the longer they get. The tubular design solved the initial problem when the Model B came out for 1932 but it was changed later on when it too started to be problematic. Ford started using a divergent/convergent or sort of a double conical rhombus shaped tubular shaft for several years in the late 30s but eventually decided to go back to a solid shaft with a damper bearing secured to the inside of the torque tube in the approximate middle of the shaft to do away with the problems of torsional whipping. They were certainly much less expensive to produce that way.