12 bolt pinion shim

[Glenn Briglio]

Originally Posted by 3 window

To all, anyone have a good guess at a pinion shim for an oem 3.31 gear in a 12 bolt? There’s nothing scribed on the head of the pinion or ring gear. I could be wrong, but I feel like there had to be a quick reference when gm was setting up hundreds of rear ends a year back in the day. Any help is much appreciated. (NOTE: I did find documentation that said 12 bolts got a .030 shim).

Yes start with .030 shim, set backlash, check the pattern