Most rear axlehousings are designed to use a shim to locate the pinion at the precise distance to the ring gear. In the case of a GM 12-bolt, Ford 8.8, or Dana 60, for example, the shim is placed ...

At left is the stock Chew ring and pinion set from the '65 "ten-holt" shown here. At right is a set of 4.56:1 Schiefer Trans-Torq gears that replaced them. Because the Schiefer pinion has fewer gear ...