12-Bolt Chevy vs. 9-inch Ford: Which is Better?
The differential case flange height in a 12-bolt varies to correctly mate the ring-gear to the drive-pinion. This saves weight but requires a costly case swap when installing gears that fall outside a given differential case range. Cases, from left: four-series (3.90:1-and-up ratios), three-series (3.07:1-3.73:1), and discontinued two-series (2.56:1-2.73:1). View Related Article
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