Four rear axle housings are used in the early Falcons. Three different size ring and pinion gear sets. The 6 3/4-inch gear is used only with the 2 and 4 door sedans, with the144 cid. The 7-inch gear is used only in taxis, Rancheros, and station wagons with 144 cid. All models with the 170 cid used the 7-1/4 inch gear. The sedan uses a 2.440" wheel (axle) bearing diameter. Taxi, Ranchero, and station wagon had a 2.677" wheel (axle) bearing diameter.
Three types of differential case are used. The two-window type is used only in 2 and 4 door sedans with the 144 cid, and is used in this housing only with a 3.10:1 ratio. The one-window case and the two-piece case are used in all four housings in all combinations with various ratios.
Two sizes of differential case pinion and side gears are used in all three cases. The side gears are not interchangeable as between the two-window case and the other two types. Pinion gear thrush washers are also not interchangeable. The side gear thrush washers, however, are interchangeable between all differential cases