[gearmesh, inc.]

When under power, you want the centerline of your pinion gear to be parallel with your output shaft of your transmission. That way, both front and rear u-joints swing in equal but opposite arcs, thereby cancelling out any vibrations. They don't have to be in line with each other, but just simply parallel. If you are making vibrations, that is energy that gets used up which doesn't get to the tires.

The variable is how much your particular suspension bushings or your leaf springs flex under power. The trick is to have an idea of how much pinion angle offset to dial in so that when your suspension flexes under power, your pinion angle is right on.

For the street/strip guys and gals, it would be recommended to have your pinion angle a little closer to ideal while cruising, and give up a little perfection while under power which would mean your pinion would be a little high while you are pouring the coals to it. Or, you could compromise and set your pinion to be a tad low while cruising, but under power it would be just a little high.

An easy way to get an angle measurement of your transmission output shaft is to put your angle finder on your valve cover. On most every engine, the top of the valve cover is parallel to the crankshaft, which is also parallel to your transmission rotating assembly centerline.

For you Fox body fans out there still using stock control arms and bushings out back, make sure you keep the pinion snubber bumper in place. You also need to keep that upper bracket part of that pinion damper weight in place. It's OK to ditch the weight, but you will need shorter fasteners to hold the upper bracket in place. The topside of this bracket is what bumps into the pinioin bumper when under power. It adds about 1/2 to 3/4 inch to the top of the rearend housing so that pinion angle doesn't rise up too much before making contact with the snubber. This will go a long way into getting your stock control arm bushings to last as long as they can. Once you go polyurethane or solid arms, you can then get rid of the pinion snubber.

For the leaf spring truck guys like Foose, those longer lowering shackles out back can be your friend. When you install these without changing your front spring eye location, your pinion angle will nose down just a little bit. That helps when you add power because you know your leafs will flex more than they did with stock power. Keep in mind, if you add caltracs, or traction bars, they will cut way down on spring windup, and you won't have to calculate for near as much pinion angle change when under power.