The History Of The Ford 9-Inch Rear End, Off-Road And Racing's Most Hardcore Axle
Some of the most durable and legendary driveline components have incredibly long histories. This is particularly true in the world of rear ends and axles, where designs like the Dana 44 have been around for more than 70 years, a testament to what can be achieved if an automotive manufacturer takes the time to do things right the first time.
So it goes with the Ford 9-inch rear end, which has been a top choice among drag racers, hot rodders, and off-road fanatics who prize durability and strength above all else. This unbreakable axle enjoyed close to 30 years of production starting in 1956, and it's lived on past its factory lifespan thanks to the efforts of and aftermarket that continues to produce almost every single component necessary to build a brand new 9-inch decades past the last factory-stamped original.
Humble Roots, Hardcore Construction
The Ford 9 inch rear end (named after the outside diameter of its ring gear) was intended to serve as the backbone for the brand's full-size sedans and trucks starting at the end of the 1950s. It was a semi-floating design (supporting the weight of the vehicle on the axles themselves) making use of a banjo carrier (named after the shape of the axle housing itself) that featured a removable carrier assembly inside the 'pumpkin.' The axles were offered in 28-spline and 31-spline form, with the latter the most popular choice for enthusiasts and racers due to their strength and ability to be shortened.
There are a number of aspects of the 9 inch rear end's design that contributed to its almost instant popularity. The unit's front-loading third member could be easily dropped out and removed when being serviced, which meant it was possible to quickly and comfortably make repairs and adjustments on a work bench, or simply slap in a replacement gear ratio without requiring elaborate disassembly of the rear end.
That same ease of service applied to the pinion shaft sub-housing (which is held in by 5 bolts versus the 10 used to secure the ring and pinion in the carrier). The nose of the pinion also features a journal that is supported by a deeply set bearing in the case itself, which adds strength while shortening the length of the pinion shaft.
All of these factors were extremely appealing in the world of motorsports, where time is often of the essence when preparing a vehicle in between runs. It was also a welcome feature for amateurs who needed to swap in a street ratio when driving home from the track at the end of the day, or for off-roaders experimenting with different tire sizes.
Of course, a rear axle setup that is easy to service is only appealing if it's durable enough to withstand the rigors of competition, and it's here that the Ford 9 inch rear end demonstrates why it remains such a compelling high performance option.
"I'd say the reason the 9-inch rear end has remained the go-to style of rear for performance vehicle is because, by design of the hypoid gear, it remains the strongest style of rear-end," says Jon Henson of Currie Enterprises, one of the world's most renowned builders of driveline components. "It still has the longest contact patch between mating surfaces of the pinion gear to ring gear. And, the added support the pinion gear has with the pocket bearing, makes it hard to break under load."
Still In The Mix After All These Years
Ford manufactured many different 9-inch rear ends over the years, and the aftermarket has picked up the same variety when putting together options. Although it's getting harder to find 9 inch axles in the scrap yard, strong parts availability makes it possible to piece together a unit at an affordable price by mixing and matching used components from the factory and reproduction parts from major manufacturers like Currie.
If anything, the market for the 9-inch is better now than it was when it was still being produced (all the way until 1986). It's possible to purchase not just full-floating versions of the axle, but even independent center sections, which boosts the number of applications for the 9-inch considerably. And then there's the virtually unlimited gear ratios available for the unit.
"The aftermarket support for gear ratios and carrier types makes the fine tuning of your drivetrain a versatile one as well," explains Henson. "You're not limited to say only 3 gear ratios, but a dozen or better, and they are not segregated by a ratio breaks in the carrier either, like say in a 12 bolt Chevy, where based on the gear ratio you'd have to pair it with the corresponding correct '4.10 and up' or '3.73 and down' unit."
Even though times are changing in certain motorsports—with NASCAR soon moving from the 9-inch it's been running for decades at every level to a transaxle design for its upcoming Cup car redesign—Ford's most durable axle shows no signs of releasing its grip among racers overall. With unmatched configurability, incredible ease of maintenance, repair, and replacement, and overwhelming aftermarket support, the Ford 9-inch is likely to remain a living legend for the foreseeable future