Driveline Angles and Vibrations info

For those with lifted trucks - don't know if this has been posted before but i found this site while looking into how 4wd works..anyway...

The solution to wrong angles is easy in theory, but not always easy in practice. There have been many good technical papers written on this subject, so I won’t go into detail now. I will however cover a few of the basics. In order for a two u-joint driveline to be free of vibration it must be in balance, and the angle of the front u-joint must be the same as, or very close to, the angle of the rear u-joint. If there is a noticeable difference in the angles there will be a vibration.
If it is not possible to match the front and rear angles, a constant-velocity joint can be used at the transfer case end with no angle in the u-joint on the differential end. Although it is expensive, and only works if the pinion is not offset side to side from the output shaft, this is the only cure in many lift situations. I have seen vehicles use a constant-velocity joint at each end of the driveline. This is more expensive but will fix any angle problem. Another solutions is to rotate the differential pinion angle up or down to match the front angle. This is usually not easy and can be accomplished with wedges, by moving the spring pads, or by rotating the axles tubes in relation to the differential center section. For some vehicles there are aftermarket kits available for lowering the transfer case or installing adjustable length control arms. Although these may seem like extreme measures, they are sometimes the only way to eliminate or lessen vibrations.
Note: If the vehicle has a differential pinion offset to the side from the center of the output shaft on the transmission or transfer case, the angles due to this offset will not cause vibration. This is because the pinion shaft and the output shaft are still parallel with respect to these side to side angles.
I have seen some lifted vehicles that vibrate no matter how much care is taken to balance the driveline and match the angles. It is one of the things that we sometimes have to live with in order to have a lifted vehicle.

here's the website: http://www.4x4now.com/4wht.htm