Ford 9-inch
This axle has been in production since the late '50s and is available in a variety of widths and housing types. Over the years, a number of different wheel-bearing designs and types of brakes have been used. Ford 9-inch guru Randy Thomas at Performance Unlimited in Hartford, Wisconsin, warns to 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.
Application: Rear.
Type: Semi-floating.
Spline count: 28 or 31.
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.
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