One issue that may arise when installing a rear suspension system on your vehicle is the angles involved in the driveline. Anything from the transmission/engine angle, to shaft angles, and the pinion angle can be of concern. I will try to cover these in enough detail so you can understand what each part does and how the interact, while making it easy to comprehend the issues at hand.

I've heard, from numerous people and shops that they just set the pinion at 2° up or down at ride height. While that may be fine and dandy on some vehicles, it certainly does not apply to all vehicles, as each vehicle has different needs and different angles. I strongly disagree with this method, and after reading this, hopefully you will understand why.

Types of Universal Joints:
We will start with u-joints and their purpose in a driveline. A u-joint, or Universal Joint, is a small (or sometimes large) cross that allows two objects (ie: transmission output shaft and driveshaft) to operate at different angles from one another and transmit the rotational power provided by the transmission. If u-joints didn't exist, then there could only be a straight line from the transmission output shaft to the pinion on the rear differential. Because u-joints help in allowing for different operating angles in the driveline, it is important to understand how they operate.

As a u-joint rotates around between the two objects its speed increase and decreases. The larger the operating angle between the two objects, the larger the speed difference will be. If there is zero operating angle (ie: the two objects are in a straight line with one another), then the speed throughout rotation will remain constant. U-joints are also lubricated when they are rotating like this. A u-joint that connects two objects that are in a straight line with one another (the operating angle between the two objects is zero) will not be lubricated, so some angle is important. This becomes an issue later on with Double-Cardan joints, introduced next.

U-Joints are also called Cardan joints. Another form of Cardan joint is a Double-Cardan joint. As the name implies, there are two u-joints in a single housing. This becomes quite helpful in some situations, but can cause issues in others. Both of those topics will be covered later in this explanation. Double-cardan joints are also known as CV joints, or Constant Velocity joints (which will become clear later).

Why angles are important:
An improperly set pinion angle will cause vibrations (noticeable or not) and will (not can, but WILL) cause premature wear on all parts of the drivetrain.

Vibration Issues:
If, after you have determined that all of your angles are correct, and you still suffer from some vibrations, then the problem could be one of many things.

The u-joints may be worn and need to be replaced.
The carrier bearing may need to be replaced.
Motor mounts may be loose or worn out.
The driveshaft could be plunged into the transmission all the way, causing a vibrating or grinding sound.
The driveshaft(s) may be bent or unbalanced.
Unbalanced tires.
Harmonic Balanacer.

And More.