Ford 9-Inch Axle: Why Racers Still Love It

The Ford 9-inch rear axle debuted in 1957 in full-size Ford passenger cars and light-duty trucks. Jalopnik reports that it was lighter than the heavy-duty truck axles drag racers had been using, easier to service, and simple to swap into other vehicles. Ford put the 9-inch in everything from Broncos to Mustangs, making it plentiful in junkyards for years.

Ford stopped making the 9-inch in 1986, but aftermarket companies still produce parts for it. Racers still use it.

What makes it strong

The 9-inch's pinion gear is supported by three bearings, an overbuilt design that keeps the gear from shifting under load. The ring gear is nine inches in diameter, giving the gear teeth more contact area. Jalopnik notes that a 6-cylinder first-generation Mustang had a 7.25-inch ring gear, while the high-output V8 Mustangs used the 9-inch.

The removable third member

Unlike many domestic rear ends, the center section holding the pinion, ring gear, and differential comes out as one unit. This lets racers swap gear ratios at the track by carrying multiple center sections. The differential itself lets the wheels turn at different speeds.

Easy to retrofit

The sheet-metal center section housing is easier to weld than cast-iron rear ends, useful for attaching different suspension points. Axle housings come in various lengths and are relatively easy to shorten, making the 9-inch fit under most cars.

Aftermarket support

Every component is available new from the aftermarket, from seals to strengthened housings. A complete new unit can cost as little as $1,500, according to Jalopnik.

How it compares

Chevrolet's 12-bolt had only two bearings on the pinion and a smaller ring gear. Ford's own replacement, the 8.8-inch axle, was lighter but not as strong and lacked the removable third member. NASCAR used the 9-inch until 2022. Until something as versatile comes along, Jalopnik says the 9-inch will keep showing up under hot rods and drag cars.

• 9-inch rear axle
• aftermarket
• drag racing
• Ford
• hot rods
• NASCAR