For over half a century, the Ford 9-inch rearend has been the king of aftermarket axle upgrades. Few other axles enjoy the same amount of bolt-on and custom componentry. The Ford 9-inch is a great swap candidate for those looking for more axle beef. It can be built to easily handle up to 42 inch tires and 1,000hp if you choose the right parts. If you are wrecking yard shopping, Ford 9-inch axles came in the rear of lots of different Ford vehicles over the years, including cars, trucks, vans, SUVs, and 4x4s. There are several different widths and lug patterns available out there. Although, the more desirable versions are getting harder to find. One of our favorites is the '74-'86 F-series and fullsize Bronco rear axle. These axles are 65 inches wide from wheel mounting surface to wheel mounting surface (a 68-inch-wide E-series van version is also common), feature the legendary 9-inch diameter ring gear, large Timken set 20 axle bearings, semi-floating 28- or 31-spline axleshafts, drum brakes, and a 5-on-5.5 lug pattern. In most cases, the ½-ton Ford 4x4s and '80 and later 2x4 pickups came with the preferred 31-spline 'shafts, which are about 34 percent stronger than the 28-spline 'shafts. All Camper Special pickups came with a beefier nodular-iron third member and 31-spline axleshafts. This third member can be identified by a large cast "N" and additional ribbing. It's not as strong as most aftermarket nodular-iron third members, but it's stronger than the more common cast third members. One of the coolest features of these junkyard axle assemblies is the ability to install massive 1.5-inch 35-spline axleshafts with bolt-on parts. However, it does require an aftermarket third member, carrier, and carrier bearings in addition to the axleshafts, which conveniently enough are equal length on the F-series trucks and fullsize Broncos. Here are a few more 9-inch build tips to help you make the swap on any 4x4.
It still requires a few specialty tools, but the Ford 9-inch is by far the easiest differential to learn how to rebuild or regear on your own. The third member can be pulled from the axle and placed on a workbench or in a vice. Pinion bearing preload, pinion depth, and backlash are all easily changed for a proper gear setup. Currie Enterprises, Ruff Stuff Specialties, Strange Engineering, and others offer completely assembled high-quality third members if you aren't up for the job of doing it yourself.
One small disadvantage of the Ford 9-inch is the low-hanging pinion. It can lead to poor driveline angles on short wheelbase 4x4s. It's not all bad, though. Because the pinion rides so low on the ring gear, there is more tooth contact between the ring and pinion. The nose bearing on the pinion also helps make it a really strong gear assembly. True Hi9 offers a high-pinion dropout third member for applications that require improved driveshaft angles. However, the gear ratio options are limited on this special application.
No other axle has more gear ratios available for it than the Ford 9-inch. You can install from 2.47:1 to 7.33:1 ratio gears on the same carrier. There is no case change. For extra heavy-duty non-street applications, 9.5- and 10-inch ring and pinion sets are available, and fit in some 9-inch axle assemblies. Lots of traction-adding differentials and spools are also available, too. Because of the 9-inch axle design, there is not a lot of real estate for the carrier, so if you are a ham-fisted driver, it's best to steer clear of really complex differentials that require a lot of small parts. They sometimes will not be as durable in a 9-inch application.
There are a few different factory and aftermarket 9-inch third members available. The Strange Engineering nodular-iron third member (left) is one of the strongest. It's made with better metal and is reinforced and gusseted in places that the stock part (right) isn't. Strange also offers an aluminum third member for those looking to save a little weight. The aluminum third member is about as strong a factory Ford nodular-iron third member, but it's also about 20 pounds lighter.
The carrier bearing size in the third member you choose will dictate the maximum diameter and spline count of the axleshafts you can run. Ford 9-inch third members come with three common carrier bearing sizes, which include 2.892-inch (28-spline), 3.062-inch (31- and 33-spline), and 3.250-inch (35- and 40-spline). Larger race versions up to 3.812-inch are available for Trophy Truck applications with 40-spline axleshafts.
The Ford 9-inch comes from the factory with a crush sleeve for pinion bearing preload. We prefer to use an aftermarket shim kit instead. We believe a shimmed pinion is less likely to get knocked out of adjustment than a crush sleeve.
At 65 inches wide, the '74-'86 Ford 9-inch from a fullsize F-150 or Bronco makes a great swap for a lot of different 4x4s. It's the perfect replacement for a later-model fullsize Ford 8.8 and the Dana 44 or AMC 20 in some Jeep FSJs. The stamped-steel housing makes it easy to solidly attach a custom link-style suspension.
All of the fullsize pickup and fullsize Bronco 9-inch axles have desirable large Timken Set 20 axle bearings. These are the bearings used by most aftermarket axle manufacturers when building custom flanged axle assemblies. TSM Manufacturing and other companies offer easy to install bolt-on disc brake kits to replace the factory drums.
Currie Enterprises, Blitzkrieg Motor Sports, Ruff Stuff Specialties, Speedway Engineering, and Tubeworks all offer custom heavy-duty axle housings in just about any width and differential offset. Spidertrax offers kit housings for those who can locate and weld the ends on themselves. Semi-float flanged axle housings are the most common, but full-floaters and front axle housings and are also available from several of these companies.
Custom-width housings generally require custom-length axleshafts. Currie Enterprises can cut, spline, and drill 9-inch axleshafts for many different lengths, diameters, spline counts, and wheel lug patterns. Upgrading from the 1.33-inch-diameter 31-spline axleshafts to 1.5-inch-diameter 35-spline 'shafts increases axle strength by 42 percent.
The iron pinion bearing supports can crack around the mounting bolts when bashed hard on a rock. We prefer to use a forged aluminum Daytona-style pinion support, available from companies like Currie Enterprises and Strange Engineering. The forged aluminum Daytona pinion support has a larger bearing on the load side and the aluminum erodes instead of cracking and breaking when it makes heavy contact with the trail. Companies such as AutoFab, Blitzkrieg Motor Sports, and Currie Enterprises offer heavy-duty race-style skidplates to protect the bottom side of your 9-inch from this kind of damage.