GM 12 bolt pinion depth/shim conversion
 

Original GM gears have a number stamped on the threaded side of the pinion gear.

Using the procedure and special tools outlined in the Chassis Overhaul Manual, shim count can be deducted. (see attached pic from 1967 manual)


My question is this:

Is there a formula that converts GM pinion codes to modern pinion depth specification? If so this will save me a LOT of time.

Adding a photo I found that may provide a clue on how to do this.

Reading the contact pattern is the only sure way of setting pinion depth for new gears. If you are setting up a used gear then the drive side contact pattern will not help you because of wear on the teeth. Usually you can go by the coast side to read the pattern and get close enough.