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History of the Ford 9-Inch

Posted in How To: Transmission Drivetrain on January 17, 2017 Comment (0)
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Photographers: Courtesy of Manufacturer

When the Ford 9-inch axle originally appeared in 1957 under the Fairlane and F-100 pickup truck, no one knew what an enduring legacy it would have. To put that in perspective, the top-of-the-line Fairlane used four-wheel drum brakes and manual steering, and made 245 hp from the carbureted FE engine. You wouldn’t swap any of those parts under your 4x4 today, but the 9-inch still enjoys incredible popularity. In fact, despite being discontinued by Ford in 1986 in favor of the 8.8 axle, there are more 9-inch parts on the market now than ever before.

We spoke to Brian Shephard, marketing director at Currie Enterprises, to get the lowdown on what makes the 9-inch so popular. While Currie offers everything from 12 Bolt to Dana 70 axles for 4x4s and hot rods, the 9-inch has been the company’s bread and butter for decades. In fact, these days, you can only order up a 9-inch from Currie that is built entirely from new parts. Conversely, you can pull a Ford 9-inch out of a truck in a junkyard and swap it under your rig for a couple hundred dollars. Most people mix and match new and used parts to get the most bang for the buck.

There are several reasons the 9-inch enjoys such a strong following. The removable third member makes gear changes much easier than Salisbury-style (Dana) axles. The use of a removable pinion support and spanners instead of carrier shims makes gear setup easy. And there are a nearly infinite number of gear ratios available for the 9-inch, from as high as 3.00 and as low as 6.50. The removable third member also means that the sheetmetal housing is not only lighter than a comparable Dana axle but is easier to weld brackets to for your link suspension since you do not have to contend with a cast centersection.

The gear design itself is responsible for the 9-inch’s reputation for holding up to high horsepower. While the ring gear diameter is smaller than a Dana 60, pinion offset from the centerline is 2 1/4 inches for a 9-inch and 1 1/8 inches for a Dana 60. This is a tradeoff, because the Dana 60 will provide a better driveline angle and more ground clearance beneath the yoke, but the Ford 9-inch will have better tooth engagement between the ring gear and pinion due to the angle of the teeth on the 9-inch design. And like a Corporate 14-bolt axle, the 9-inch has a third pinion bearing beyond the pinion teeth that minimizes gear deflection.

All of this adds up to an axle that has endured for more than half a century and shows no signs of fading into obscurity any time soon.

Ford 9-Inch Advantages
• Removable third member
• Third pinion bearing
• Pinion offset
• Sheetmetal housing
• Strong aftermarket support

Ford 9-Inch Axle Widths (in)
• 1965-66 Mustang, 57.575 inches
• 1966-77 Bronco, 58 inches
• 1978-86 Bronco, 65 inches
• 1974-86 F-150, 65 inches
• 1972 E250 Van, 68 inches

Ford used a variety of housings over the years, and Currie offers all of them as upgraded reproductions, as well as housings of their own design. The earliest housings used in cars through the mid-1960s were the weakest, with abruptly ending butt-welded carrier centers to tubes and a smooth backside. Later housings appeared in 1966 with stronger tubes and the familiar “hump” in the middle of the housing. The later truck housings received even beefier center housings that extend farther into the tubes for more strength.

The 9-inch ring-and-pinion use a hypoid design that puts the pinion gear in contact with the ring gear at the bottom of the gear. This results in more tooth engagement and a stronger gearset. The 9-inch also does not use a carrier break, as Dana axles do, so if you buy a locker when you have 3.73 gears it will still work when you gear down to 4.86s.
The Ford 9-inch uses a third pinion bearing on the front of the pinion in the third member housing. This is similar to a Corporate 14-bolt axle, and essentially eliminates gear deflection when under load. This the gear equivalent of mounting a suspension component in single sheer versus double sheer for more strength.
Different pinion cartridges have been available from the various production years and models. The Daytona-style cartridge (right) allows for a larger pinion head bearing than the standard pinion cartridge does. Currie offers both nodular iron and aluminum pinion supports to fit any application and budget.
From left to right are a factory gray iron case, a stronger “N” case, and an aftermarket Strange case. The “N” cases had two vertical ribs, three horizontal ribs, and a machined-in fill plug, but they are getting difficult to find. Currie offers an affordable reproduction “N” case that eliminates the need to scour the local wrecking yard.
Currie offers aftermarket third members with larger differential bearings. These are mandatory when upgrading to larger axle shafts (such as 1.5-inch, 35 spline axles) since the larger bore allows the bearing size to increase relative to the axleshaft.
A variety of yokes are available for the 9-inch. Most factory yokes use 1310 or 1330 U-joints, but aftermarket yokes are available for 1350 U-joints and U-bolts instead of straps. The yokes are dependent on the pinion support that is used (generally referred to as “long” and “short”). Flanges are also available for those who prefer them to traditional yokes.
The offset nature of the 9-inch pinion means that the axleshafts will be different lengths when the pinion is centered. On the plus side, you will never get confused about which axle came out of which side, but the downside is that if you want to carry spare axleshafts you need to carry two.
The 9-inch axles found in most Ford cars use 28-spline axleshafts. Trucks had 31-spline axleshafts starting in the mid-1970s, and they are much stronger. The 35-spline axleshafts are also available but require a new third member with larger carrier bearings.
A variety of housing ends and bearings were used over the years. The small bearing housing ends (left) use 9/16-inch socket size nuts with 3/8-inch bolts. The late model (often referred to as Torino) housing end (center) are the standard used on aftermarket housings, they also use a 9/16-inch socket size and 3/8-inch bolts. Early large bearing housing ends can be found on junkyard axles, they use 3/4-inch socket size nuts and 1/2-inch bolts.
All 9-inch axles found under trucks and Broncos came from the factory with drum brakes. Most of the 9-inch axles under cars had drums as well, with the Lincoln Versailles being the notable exception. The Versailles axles are fairly rare though and use a 5x4 1/2 bolt pattern, unlike the truck axles, which use a 5-on-5 1/2 bolt pattern. Currie Enterprises offers disc brake kits uses Explorer components that can be used with industry standard Torino housing ends.

Sources

Currie Enterprises
Corona, CA 92880
714-528-6957
http://www.currieenterprises.com

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