Good stuff! But those shafts are more complex than our single shaft with a u-joint at each end.
U-joint operating angles are generally the most common cause of driveline vibration in vehicles that have been reworked. When reworking a chassis or installing a new driveshaft in a vehicle there are basic rules that apply to U-joint operating angles that you should follow.
Number-1: U-joint operating angles at each end of the shaft should always be at least 1-degree.
Number-2: If you are to achieve cancellation these U-joint operating angles on each end of a driveshaft should always be equal (within 1-degree), but opposite of each other.
Number-3: U-joint operating angles should not be larger than 3-degrees. If they are, make sure that they do not exceed the maximum recommended angles.
To set up the driveline you need to establish the angles for the transmission output shaft, rear end pinion shaft and driveshaft. A good tool for measuring these angles is an inclinometer. They can be obtained quite inexpensively from a local parts store or tool supplier.
First measure the transmission output shaft angle. It should be pointing downward to the rear with the vehicle sitting at ride height on a level surface. At least 1-degree and ideally not more than 3-degrees down. You can alter the transmission angle by inserting or removing shims under the rear transmission mount.
Next step is to measure the rear end pinion shaft angle. It should be pointing upward towards the front with the vehicle sitting at ride height on a level surface. At least 1-degree and ideally not more than 3-degrees up. You can alter the rear end pinion shaft angle by inserting or removing wedge shaped shims under the rear spring mounts.
Finally measure the driveshaft angle to confirm that it is at least 1-degree down from the transmission output shaft angle and at least 1-degree up from the rear end pinion shaft angle. Achieving these angles in relation to each other will cancel out the vibration.
Checking to see if you have got it correct:
If there is no vibration under normal operating conditions then the angles are correct.
If there is vibration under acceleration, you need to add more downward pinion angle preload. If the opposite occurs, the vibrations tends to decrease or disappear under acceleration, you need to reduce the downward angle preload.
If the vibration steadily increases with driveshaft speed (either accelerating or decelerating) the symptom is primarily the result of a driveshaft imbalance or yoke runout. Sometimes this yoke runout problem can be improved by rotating the U-joint 180-degrees in the rear end differential yoke.