When the Ford 9-inch axle originally appeared in 1957 under the Fairlane and F-100 pickup truck, ... pinion offset from the centerline is 2 1/4 inches for a 9-inch and 1 1/8 inches for a Dana 60.

The Ford 9.000-inch ring gear has a size advantage over the 12-bolt's 8.875-inch ring gear, though not by that much. The Ford's larger ring gear, in addition to its greater offset relative to the ...