Measuring Pinion Angle:
There are many different ways and opinions so this is just a simple small write up that usually works very well for street/strip cars. Thanks to Steeda!
Pinion angle is the difference between the centerline of the driveshaft and the centerline of the pinion shaft of the differential. To measure it you must be able to work under the car with the suspension fully loaded and the car level. A drive on lift works best for this.
Method "A" - (recommended) Use an angle measuring gauge (adjustable protractor) to measure the difference between the pinion flange and the drive shaft directly. These gauges are available for under $10 from a hardware store. Place the edge of the gauge vertically against the front of the pinion flange, beside the driveshaft. Extend the measuring arm forward parallel to the bottom of the driveshaft. Extend a straight edge under the driveshaft to the measuring arm of the angle gauge. Hold the straight edge flat against the bottom of the driveshaft and adjust the measuring arm to read the angle. Depending on the gauge you use, you may have to subtract 90° from your reading to get the correct number. Your final measurement should be between 0 and 5. Examine the diagram at the bottom to determine if the pinion angle is nose up or nose down.
1) Use a gravity angle gauge (Available at hardware stores) to measure the angle between the driveshaft and the
ground. Hold the gauge on the bottom of the driveshaft. Align the gauge front-to-back under the car in line
with the driveshaft and read the number from the gauge. Write down this number.
2) Next, hold the side of the gauge against the front of the pinion flange (beside the driveshaft). Measure the
angle between the pinion shaft and the ground. Write down this number.
3) Subtract the first number from the second number. This is your pinion angle. Examine the diagram at the
bottom to determine if the pinion angle is nose up or nose down.