Ford 9-Inch
Application: Rear
Type: Semi-floating
Axle Shaft Diameter: 1.19 and 1.33 Inches
Spline count: 28 or 31
Ring Gear Diameter: 9 Inch
Factory ratios: 2.50:1 through 4.56:1
Maximum tire size for stock axle: 37-inch
Strong point: Removable third member allows for easy upgradeability, can upgrade to larger-diameter pinion
Weak point: Difficult to remove third member if an axleshaft breaks, stock pinion-shaft diameter is smallish
Junkyard jewel: They're hard to find, but some Ford ½-ton 4x4 pickups were equipped with an optional nodular-iron 9-inch, which was stronger and offered less chance of bearing-cap failure
Building secrets: Replace the crush sleeve in the pinion bearing with solid spacers and shim kit. This eliminates the movement of the pinion shaft under hard load
Aftermarket alternatives: Currie Enterprises, Custom Differentials, DTS Custom Service, National Drivetrain Inc., Randy's Ring & Pinion
Notes: be careful when hunting for a 9-inch in junkyards because they are cosmetically similar to the weak (and expensive) Ford 8-inch axle. Also beware of the 9 3/8-inch axles in Lincoln cars because they also look similar but take a different axle length on one side due to their slightly offset housing.