Ford 9 Inch Axle - Knowing The 9-Inch

Another area where the 9-Plus is beefier than the stock 9-inch is in the carrier bearing caps. The 9-Plus caps (right) are thicker and double-ribbed for greater strength.

Another area where the 9-Plus is beefier than the stock 9-inch is in the carrier bearing c

The 9-Plus Axle
Individuals scrounging salvage yards for 9-inch axles can still find plenty to choose from (See the accompanying sidebar "Junkyard 9-Inch Tips"), but for a company like Currie, which buys big lots of axles to refurbish, the supply is starting to dwindle. Not only that, but Currie tells us the quality of the 9-inch axles out there is falling. "New 9-inches were last used in cars in 1981, 1986 in trucks. That's 20 years ago. Imagine how beat up these axles are now, especially those coming from the north and east, where they salt the roads," he says.

So Currie decided to manufacture brand-new 9-inch components-housings, axletubes, gear cases, and so on-and called them the 9-Plus line. The "Plus" comes from the fact that, while these assemblies mirror Ford's original design, many of the components are beefier than the originals. The housings, for example, are made from 0.200-inch-wall forming steel, while the wall thickness of a stock 9-inch housing was 1.77 inches. The 9-Plus gear cases are made from nodular iron, while the stock cases were made from what Currie calls "gray steel." The carrier bearings on the gear case are 3.062 inches in diameter, compared to the stock 2.835 inches. There's more material around the pocket bearing, the ribs on the gear case are thicker with bigger feet, and the list goes on.

But in several critical dimensions, the 9-Plus is identical to the standard 9-inch, which means many parts are interchangeable. You can even bolt a 9-Plus gear case to a standard 9-inch housing.

Whether you're thinking about buying a refurbished standard 9-inch or a brand-new 9-Plus, you're looking at a custom setup. "There are so many options available for this axle that we can't really put built 9-inch axles in stock," Currie told us. Instead, his sales team spends a lot of time assessing each customer's needs-what they're driving, how they'll use the rig-and then recommending the right combination of housing, carrier, gear ratio, spline count, traction aid, and so on that best suits the individual vehicle.

Look closely and you can see the differences between the 9-Plus gear case (right) and a refurbished stock 9-inch gear case (left). The reinforcing ribs are thicker, as are the feet where they join the case. There is also more material around the pocket bearing. What you can't see is the case's construction. The stock pieces were made from gray steel, while the 9-Plus cases are made from nodular iron. Ford made nodular iron cases, too, for high-performance applications in the Sixties and Seventies, but they're getting scarce.

Currie Enterprises has begun manufacturing brand-new 9-inch components. These new axle assemblies are called the 9-Plus line, and they're dimensionally identical to stock 9-inches in key areas so you can swap components-ring-and-pinion sets, gear cases, and so on-between them. Here, a stock 9-inch housing sits behind a 9-Plus Heavy Duty housing. The new housings are made from forming steel that is thicker than the original piece, and they will accommodate 3-inch-diameter tubes that can slide into the housing up to 4 inches.

The Bottom Line
Because of the wide array of choices, establishing a price for 9-inch axles is difficult. But since Currie told us the 9-inch represents excellent value, we pressed him on the issue to find out what value actually meant.

To find an answer, he set up price quotes for three different front and rear axle combinations, using similar components in each system, to make it as close to an apples-to-apples comparison as possible. Our subject vehicle would be a hypothetical rockcrawling TJ.

In the rear we chose between a Dana 44, a Currie high-pinion 9-inch, and a reverse-rotation Dana 60. All three would have 4.56 gears, Detroit Lockers, and Explorer disc-brake upgrade kits. Though we tried to make the setups as identical as possible, there were differences. The 60 contained a TeraFlex ring-and-pinion set and 35-spline axleshafts, while the 44 and 9-inch were comparable with 30- and 31-spline axles, respectively. As it turned out, the prices were closer than we imagined. The 44 came in at just over $2,800, the high-pinion 9-inch was pennies under $3,000, and the 60 cost a tick above $3,700.

The differences between front axle assemblies were more pronounced, but that's because we tossed in an additional variable: steering knuckles. Big tires are going to put big stress on the stock steering system, so many hard-core 'wheelers are upgrading their steering with more powerful boxes, hydraulic rams, and other accessories. In this situation, the weak link becomes the steering knuckles. For the ultimate in knuckle beef, you can graft F-450 Super Duty pieces onto your axle, but it'll cost you.

For our imaginary TJ, we asked for three frontends: a reverse rotation Dana 44, a Currie high-pinion 9-inch with 31-spline Spicer outers, and a hybrid with a Currie high-pinion third member matched to a housing that would accommodate the Super Duty knuckles. Again, all three would have 4.56 gears and traction aids, though in this example the first two combinations were fitted with ARBs, while the Super Duty 9-inch had a Detroit Locker. Another difference: The 44 and high-pinion 9-inch had 30- and 31-spline Spicer axles, respectively, while the Super Duty shafts were 35-spline.

Would you be surprised to learn that the Super Duty parts nearly doubled the assembly's price? Here's how it worked out: The Dana 44R cost $4,100, the Currie high-pinion 9-inch was $4,200, and the Super Duty 9-inch went out the door for $6,190, thanks in large part to the $2,300 cost of the Super Duty parts by themselves.

Have we seen the end of upgrades for the 9-inch? Not likely. As long as these axles are popular and plentiful, engineers are bound to continue to mess with them, to bring their strength and durability up even further. Will a seriously beefed 9-inch be able to replace a Dana 60? No. But the seriously beefed 9-inch does present a worthwhile alterna-tive for the 'wheeler who's not ready to move up to 1-ton equipment.

Junkyard 9-Inch Tips
If the prices of the new 9-inch axles mentioned in this story leave you gasping for air, you'll be pleased to learn that there are still plenty of used 9-inch axles to be found in salvage yards all over the country. They're going to be old and grimy, but if you shop carefully, you can find a perfectly serviceable unit for a budget-oriented 4x4.

For tips on buying a used 9-inch, we spoke with Bob Carlisle at Bob's F-100 Parts (909/681-1956). Bob's specialty is classic Ford pickups, not necessarily 4x4s, but he uses dozens of 9-inch axles in his chassis and knows how to rebuild them.

"As long as there's still oil in it and the pinion seal hasn't blown, the axle will be OK," Bob told us. "The 90-weight in the pumpkin is so thick it will coat the gears and keep them from rusting." If the front of the housing is covered in oil, you've got a blown seal. Rust on the external parts shouldn't be an issue, as long as it's just surface rust. Stay way from axlehousings where they coat winter roads in salt.

Keep in mind that 9-inch axles were used under cars and trucks, so pick an assembly that came from a truck for its bigger axles and bolt pattern. Rebuilding a junkyard 9-inch is pretty simple, Bob says. "I pull the axles and open the pumpkin, replace the gaskets, put new seals around the axles and the yoke, and occasionally change bearings. That's about it."

Prices for a salvage 9-inch vary. Bob's experience reflects the Southern California market. "Go to a pick-your-part kind of yard, where you remove the axle yourself, and you can pay as little as $100 or $150. More if the axle has disc brakes." Add a couple hundred dollars if the yard does the removal for you. The most expensive junkyard 9-inch? "The one out of a Lincoln Versailles. Remember it, it looked like a Granada? It's popular with hot rodders because it's narrower and has disc brakes. That'll cost $500-plus," Bob said.

Relative Strength
We asked Ray Currie for a thumbnail sketch of where the most popular 4x4 axles ranked in terms of relative strength.
His list (from weakest to strongest):
Dana 30
Dana 35
AMC 20
Dana 44R*
Dana 44/GM 12-bolt
Currie High-Pinion 9-inch
9-inch
Dana 60R*
Dana 60
Dana 70/GM 14-bolt
R denotes reverse-rotation