Shays and Universal Joints

Shays use universal joints.
Universal (aka Hookes or Cardan) joints have two fingers from each shaft (called a yoke), joined at 90 degrees apart. Shays have the bearings between the yokes in a ring ouside the joint whereas autos have the bearing inside a plus shaped block inside the joint. Both yokes can swivel in the bearing, maning it can attain an angle at any point in its rotation. however, the power transfer is not uniform.
A CV joint (Rzeppa joint) uses a ball and socket. Both have a series of slots, the ball on the outside and the socket on the inside, parallel to the shafts. Ball bearings ride in the slots and transfer power while rolling in the slots to allow the shafts to reorient as they turn. It functions much like a set of bevel gears but is better when the angles vary. The Rzeppa joint was invented in 1926, a bit late for Shay adoption. It also has a more limited lifespan than a U joint and must be kept sealed by a rubber boot to protect it. It is more complex and so more vulnerable to failure. U joints will last the lif of a car un normal service. Rzeppa joints will go in 100k-150k miles.
This URL has some nice pictures of the guts of a Rzeppa CV joint (see page 4):
[www.mscsoftware.com]
There are other types of CV joints like Tripod which are variations on the Rzeppa.
Again, I'm not an expert in this. I just happended to bone up on it a few months ago when I had to replace a couple axles in a Toyota.