installed SS springs and pinion angle is at 0
That's the way I do it. There have been times where it didn't work out well and the chassis book method was employed.
If you go more than about 4* down on a street car you run the risk of some vibration issues. I've had SS sprung cars that needed more than 8* down to work well, but they weren't street driven, race only.
The transmission measurement is to get the centerline. The reason to adjust the pinion to -5 below centerline is because the leaf springs are going to allow the rear end to lift 5 degrees. After they lift 5 degrees it should be parallel to the trans. Right now my trans is at -1 and the rear end is +1 meaning it is a perfectly parallel. In order to get -5 down pinion angle the rear end will have to be positioned to -4 degrees down instead of +1 (1-5= -4) Once the -4 degrees is reached when I smash the gas and the pinion lifts 5 degrees the driveline is parrallel.
That's the way I do it. There have been times where it didn't work out well and the chassis book method was employed.
If you go more than about 4* down on a street car you run the risk of some vibration issues. I've had SS sprung cars that needed more than 8* down to work well, but they weren't street driven, race only.