[Cobra20646]

Shaun,

To add to Campy's post.....

The center lines of the transmission yoke and the pinion yoke should be parrallel non intersecting lines. When rotating, the U joint does not rotate in a circular mannor, but rather in an elliptical pattern (each joint rotates this way). When properly installed, (parallel non intersecting) the elliptical motions are canceled out, and smooth, rotation occures.

Another important thing to consider is the angle between the two U joints. Too much angle can cause binding and eventual failure of the joint. If my memory is good (?), angles of 12 to 14 degrees can be safely handled. I understand that vehicle manufactures strive for angles not to exceed 7 degrees.

The amount of distance between the two parallel lines becomes important when considering the length of the drive shaft. A longer drive shaft can tolerate more "offset" than a shorter one to maintain the same drive shaft angle.

Also, there can be two offsets. One in the vertical plane and another in the horizontal plane to further confuse the builder. I believe simply adding these two angles together will provide you with the total angle that must be in the 12 to 14 degree range to be satisfactory.

An IRS is easier to design for as there is no change in the drive shaft angle during suspension travel. With a live axle, you must consider this travel in your calculations so as not to put the U joint into a binding situation when the axle is at pushed to its limites.

Im drawing this from memory....... somewhere in my files at home I have the reference material and web sites from which they came. I'll post them later if you would like them.

I hope I didn't add to your confusion ;-)

- Jim -