2/4 drop pinion angle shim this - shim that?

[derek_silverado]

Ok, looking to do a 2/4 drop. I hear that a 4 inch drop may cause some vibration. True or false? What exactly is a pinion.... what is a shim? what is this angle and why is it important? Is it easy to adjust help, im a newb.

[droppedgmc]

"pinion gear" is the end coming out of the rear end hooking up to the drive shaft. when the truck is lowered the pinion angle goes down. by adding the "shim", it rotaes the angle up. a slight angle, very slight angle is the best to have. on a 2/4 drop, the most needed would be a 2* shim. they are placed between the springs and the rear end