[Keith Seymore]

There are two u joints in the shaft, each generating accelerations and decelerations as they rotate (two kicks per rev of the shaft).

The u joint working angles at each end need to be equal and opposite in order for those forces to cancel out.

K

[Keith Seymore]

Originally Posted by Keith Seymore

There are two u joints in the shaft, each generating accelerations and decelerations as they rotate (two kicks per rev of the shaft).

The u joint working angles at each end need to be equal and opposite in order for those forces to cancel out.

K

Additionally, the u joints don't care about the orientation of the individual components or the frame or the ground: only the difference between the two.

The vehicle could be on its side and the u joint working angles would be the same*.

K

*barring any changes in suspension compression, of course.

K

[johnta1]

You want the engine plane and the rear end plane to be the same.

That was supposed to be in parallel. The same angles.
If there is a left or right (as looking from top instead of side) angle difference that is also another can of worms. (like front axle on 4 wheel drive, leave that for Keith)