i have always been un sure of how the pinion angle should be set and i never get the same answer some people tell me to set it straight with the drive shaft some people say it needs to be at an angle . i stopped at my buddys shop and ask him what he does with his pinion angle ..and he told me he always sets it paralle to the ground .he said hes never had any problems with vibration and unnessecary wear .but this method sounds like a primative solution that alot of folks seem to have trouble with . what do you guys do about pinion angle ?  

proper way is to set it about 1-3 degrees down because when you accelerate hard the pinion will want to rotate upward a tad. You might get away with being the same as the tranny if it is not a high horsepower vehicle, but 1-3 down is a good way to go  

it is supposed to be in line with the crankshaft of the motor when it is under load. So the 1-3 degrees is a good method. Im doing the pinion angle on the buick right now. Im pushing about 400 horses, so imma be a tad above. depending on your rear suspension setup, you may have a pinion angle change that is major. my three link setup will have quite a bit of change, but you should set the pinion angle for what you believe is ride height. ie when you are running in aparking lot and you hit the switch to full droop, the pinion angle is not going to be that significant...unless of course you are doin some burnouts and stuff.  

1-3 degrees down from what ?  from being level with  mother earth ? from being straight with the drive shaft ? from stock position ?  

level with the crankshaft  

Remember this for other applications though.
Reason: Some face up.
The pinion is the angle from the tranny in relation to the differential angle.
Meaning put a angle finder  on the end of the tranny,  most will face up  some wheres of 1 - 3 deg.
so the differential should face down 1 - 3 deg.Making the line of symmetry parallel.So It depends on what kinda vehicle.
Try to create a straight line from the back of the crankshaft through the transmission, driveshaft, and the pinion of the differential—under load.Because the pinion goes up with load its best to set it with some angle when its at stock height and no load.Not just parallel to the ground.
Which is why they tell you to point it down.It helps eliminate wheel hop,so make sure its set right Especially if your up'ing the ponies homie.