The Stovebolt Site Forums The Shop Area Driveline Pinion angle

Is the pinion angle 3 degrees down or 3 degrees up? If it makes a difference I've installed a 10 bolt on my '50 3100. Obviously, I've never set a pinion angle but I know its required. Is the angle then off of the transmission the opposite? Asking to learn.
What is the reason for having angle between the two?

The angle of the pinion needs to be parallel with the transmission output shaft. They can be colinear, which is ideal, but probably not really practical in most cases.
So if the angle of the engine transmission is 3 degrees (trans lower than the engine), the pinion needs to be 3 degrees up to make it parallel.
The reason is to minimize vibration. If the transmission and pinion aren't parallel, the driveshaft will tend to vibrate because of the action of the u-joints.

This topic can turn into a real can of worms so be ready.

The pinion angle should not be adjusted with full weight of the truck on the springs with the truck on the ground in " as driven condition " .

The pinion should be close to parallel to the crankshaft

The u-joints should have a working angle of more then 1 to 3 or less degrees ideally, but more or less will still work. .

3 degrees is a standard starting point, but not set in stone. Lots of 4x4s have drastic angle drivelines, and lots of cars came with very little angle

Long leaf spring can twist under heavy loads, so adjust for that with more pinion angle if this is working truck ( when twisted under load, the pinion would be in the correct position ) 1 more then crankshaft

I forgot to mention that part. Very critical.

I was taught to get the two as parallel as possible and then add one negative degree to the differential side so that spring wrap-up (which will happen) won't put your differential angle less than your transmission angle. Oh, and measure on machined surfaces. That hasn't been mentioned yet, but I think it ought to be. I did this not very long ago on a 3100 with everything new...springs, mounts/shackles, everything new and all stock height. The transmission angle was +3 degrees and a hair, so the differential was set at -4 degrees on the nose. Good luck. As Joe said, this can be a can of worms.

I changed my post above, it should be WITH full weight on the axles. Auto-correct or poor eyesight, not sure which one.

If you keep the u-joint working angles around 3 degrees at both ends, you won't have any problem. The rear u-joint angle is always changing as you drive, way more then front, so being dead on is not all that important, get as close as practical and call it a day. The working angle of a u-joint is measured from output shaft to driveshaft, and driveshaft to input shaft. This eliminates any error in measurements when the truck is not level.