I do know a couple engineers who graduated with honors and can engineer circles around me. They simply love machines. I know a few mechanical geniuses who never went to college. Unfortunately, I know far more who don't love what they do, I had to help one put the chain back on his bike when we were engineering seniors.
When I was young I noticed the universal joint in my Dad's socket set didn't produce a smooth rotation when it worked through an angle. It went fast-slow-fast-slow, changing every 90 degrees. Years later our formula car trashed it's axles in college, and I wrote my senior paper on how pairs of universal joints out of phase work to produce a smooth rotation. We had put them in phase.
The fast-slow-fast rotation caused by a u-joint at an angle can be neutralized by another u-joint 90 out of phase working at the same angle. 90 out of phase u-joints have the yokes on the driveshaft oriented the same, as on our rear driveshafts. The u-joints are mirror images of each other. The rear axle moves up and down keeping the input shaft parallel to the ground, and parallel to the shaft coming out of the t-case, so the two u-joints always work through the same angle.
Our front driveshafts have very little angle, especially at the front. The axle pivots from near the rear u-joint as it goes up and down, so the front u-joint doesn't change angle much. It looks to me like they have a mostly vertical angle at the rear, and slight horizontal (sideways) angle at the front. Since they work through angles 90-degrees off from each other, they really are out of phase even though the u-joints are oriented the same. This should be smooth on a stock truck going down the highway, the two angles are about the same. At axle extension the two angles aren't the same, but you'd go slow in those situations and not notice any vibration. Unless you have a lift.
