WHAT TO LOOK FOR IN A THIRD MEMBER
WHAT TO LOOK FOR IN A THIRD MEMBER
The Ford 9-inch continues to live a healthy life.
DESPITE LAST BEING OFFERED UNDER A PRODUCTION vehicle in 1986, the Ford 9-inch continues to live a healthy life thanks to its light weight and abundant ground clearance. Not all 9-inch components are equal though when it comes to strength, or price for that matter. To illustrate the bevy of options, we recently took a factory third member and compared it to an aftermarket third member from G2 Axle & Gear and a money-is-no-object third member from Gearworks. All three were fitted with ARB Air Lockers, but even the selectable locking differentials are not created equal.
At the beer budget end of the spectrum, we used a factory 9-inch third member and the original pinion support and 1310 yoke. To that we added 4.88 gears and a 31-spline ARB Air Locker (PN RD119) to work in conjunction with factory big bearing axleshafts. The standard case is not as desirable as a nodular case, but it is far more common. If you set up the gears yourself, you can have a similar setup for around $1,200 that will live a long life behind a mild V-8 and 37-inch-tall tires.
With more engine, bigger tires, or a heavy rig, the factory parts might not be strong enough. The 9-inch benefits from huge aftermarket support though, so much so that it can be overwhelming. We built a third member with entirely new parts from G2 Axle & Gear and ARB that is significantly stronger than the factory third due to better materials and bigger bearings, but it also cost us twice as much money. We spent our money on a G2 third member (available
in either aluminum or nodular steel), stronger “Daytona” style pinion support, a G2 ring-and-pinion, and a full install kit with Timken bearings. The G2 Axle & Gear components were paired with ARB’s RD99 Air Locker, which is similar to the RD119 except it accepts larger,
11⁄2-inch-diameter, 35-spline axleshafts, making it well matched to chromoly axleshafts and fabricated 9-inch housings that are regularly found under buggies and hardcore rockcrawling rigs.
If you own a Trophy Truck or Ultra4 car, or simply must have the very best, it’s time to look at Gearworks components. The Gearworks third member is designed to accommodate a larger, 10-inch ring gear for increased strength with no penalty in ground clearance. The case uses huge, 4-inch bearings than can accept axleshafts up to 2 inches in diameter.
We bolted the 10-inch ring gear to ARB’s RD99CE competition Air Locker. “We love a challenge,” ARB USA President Doug Pettis says. “There’s only so much room inside of a 9-inch housing, so in order to increase the case strength by 290 percent we had to get creative with regards to design and materials.”
The result is the strongest selectable locker ever offered for the
9-inch axle thanks to deeper tooth engagement and forged internals. Again, the price roughly doubles from the G2 components and RD99 Locker, and is four times higher than our rebuilt junkyard third member.
Which third member is right for you depends on a variety of factors, including your budget and intended use. The beauty of the
9-inch is that you can mix and match parts under your rig, upgrading as components fail or your budget increases. Even though the
9-inch hasn’t been found under a new Ford in decades, this axle isn’t going away any time soon.
3 3Different-sized bearing caps are available from the aftermarket. The stock case uses 3.062-inch bearings that are well matched to the original 28- or 31-spline axleshafts. The G2 third uses 3.25-inch bearings that accept 1.5-inch, 35-spline axleshafts. The Gearworks third uses huge,3.812-inch bearings that support up to 2-inch, 45-spline axleshafts.
6 6Here is a closer look at that third pinion bearing that the 9-inch is famous for. In addition to there being more material, the type of material is also a factor in strength. Gray iron has a tensile strength of 30,000 psi, while nodular iron is 65,000 psi.