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 This is the C7AW-E 9-inch...  This is the C7AW-E 9-inch case with the single 12/6 o'clock rib. What gives this case strength is a high nodular-iron content and meatier pinion pilot support. Also expect to see C1AW and C4AW on this case in your travels. |
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 The "WAR" case, used from...  The "WAR" case, used from '57 through the early '60s, is identifiable by its two-vertical-rib design, which makes it look a lot like both the '67-and-up 8-inch case and "N" case 9-inch. However, the 'WAR" case has a low nodular-iron content, making it weaker than the C7AW-E case just mentioned. The pinion pilot support is also thinner, making it more prone to failure. Avoid this case. |
 Currie Enterprises built a...  Currie Enterprises built a 9-inch rearend for our own Project Ed '65 Mustang 5.0L EFI hardtop a few years ago. Currie specified the C7AW-E case for our 3.55:1 Richmond Gear differential, which remains in reliable service many years later in the Dallas-Ft. Worth area in private ownership. |
 This is a 9-inch "N" case...  This is a 9-inch "N" case rebuilt by Currie Enterprises with a Currie pinion support for greater strength. |
 The "N" case employs a high...  The "N" case employs a high nodular-iron content to get its strength. There's more iron everywhere, including the pinion pilot support and side caps. |
 This is a typical 9-inch pinion...  This is a typical 9-inch pinion support, without the cast-in guard. The "DIF" means Dearborn Iron Foundry. There is also a bolt-on, stamped-steel yoke guard available for this pinion support in applications where a guard is necessary. |
 Here's the cast-in guard pinion...  Here's the cast-in guard pinion support. |
 Matter Of O' Pinion When you...  Matter Of O' Pinion
When you are exploring 9-inch differentials out there, you're going to hear two-pinion and four-pinion. A two-pinion 9-inch differential is generally seen as a light-duty piece. Four-pinion differentials, more common with Limited Slip, Equa-Lock, and Traction-Lok, have more internal support, which means a four-pinion unit is more suitable to high-performance applications. |
9-Inch Fact And Fiction
The 9-inch Ford differential needs little introduction for seasoned enthusiasts. Most of us understand that it is the strongest differential ever made for Fords and other vehicles alike. NASCAR racers love it for its integrity--which means it sees use with the Chevy boys as well. The 9-inch Ford outperforms the GM 12-bolt rearend by a wide margin. It has found a near equal in Chrysler's Dana rearend, which is a proven performer. But when push comes to shove, racers opt for the 9-inch Ford. Street-rodders love the 9-inch Ford for its easy-to-service design and ability to take punishment.
The rough and tough 9-inch Ford was introduced in 1957, and it didn't change much in appearance throughout its production life. What it did do was improve as horsepower ratings and demands increased. Likely the greatest changes came during the early '60s, as the horsepower wars heated up.
In the beginning, there were 28-spline axleshafts and small axle bearings. And this remained the basic standard throughout the 9-inch Ford's production life. As this design evolved, Ford made solid improvements, such as a four-pinion carrier, Limited Slip, Equa-Lok, and Traction-Lok, larger axle bearings, and 31-spline axleshafts. Ford also produced a much stronger nodular-iron case, known as the "N" case, for high-performance applications. You'll find the "N" case in Boss 302s and Boss 429s, for example. Sometimes, you'll find it in 428 Cobra Jet "Drag Pack" Mustangs as well. The earliest "N" applications were 406 and 427ci big-block Galaxies in '62-'63.
The 9-inch Ford differential is easy to understand. Choosing the right one for your mission is also easy. It just isn't always cheap. Much depends on what you find, where you find it, and what your needs are. The most common 9-inch differential case is the C1AW-C, C4AW-A, C4AW-C, and C7AW-E casting, easily identified by its single-rib design. This casting has a single rib that runs from 12 to 6 o'clock, flanked by three cross ribs. Think of this casting as the basic 9-inch carrier, used from the early '60s through the early '80s. This is a durable 9-inch case, used in a host of Fords ranging from big-block Fairlanes and Mustangs to fullsize Fords and pickup trucks. The most common version of this casting is C7AW-E, used from '66 through the early '80s. Expect to find this casting in a lot of 9-inch housings from '66 through the early '80s. Hot spots are big Fords and pickup trucks.
Another fairly common 9-inch case is the "WAR" casting, with two 12- and 6-o'clock ribs, very similar in appearance to the smaller '67-and-up 8-inch case, and the heavy-duty 9-inch "N" case. The "WAR" case doesn't employ the high nodular-iron witnessed with the C7AW-E case mentioned earlier. The "WAR" case pinion pilot support doesn't have as much iron either, making it more prone to failure. The "WAR" case is more common with the earliest 9-inch axles from '57-'65. The C7AW-E single-rib case is common from '67 and up, making it more plentiful. We have also seen the single-rib casting with different numbers--C1AW-C, C4AW-A, and C4AW-C--indicating an early '60s origin. This makes the C7AW, C1AW, and C4AW single-rib case quite common.
There is also the "WAB" case, which is similar to the "WAR" case in appearance. Where the "WAB" case differs is differential side bearing size (3.063 inches in diameter). The "WAB" case isn't shown here. The most common 9-inch differential side bearing size is 2.892 inches in most applications.
Another area of interest is the front pinion support. We have seen several variations and casting numbers in our travels. Expect to see some pinion supports with a guard cast into the piece above the yoke. This guard is designed to keep the spinning driveshaft yoke away from the chassis bounce-back bumper whenever the vehicle bottoms out in a dip. With some vehicle applications, this is not a concern--in which case, the cast-in guard will not be present. Mustangs, for example, need the pinion support with the cast-in or a bolt-on guard. The cast-in guard was not used when the bolt-on guard was used.
The most common pinion supports we see out there don't have the cast-in guard. Expect to see C0AW-A, C5AW-A, C6AW-A, C7AW-C, D2AW-A, and D2SW-C. The C7AW-C pinion support has the cast-in guard.
The highly sought-after 9-inch "N" case was born of a need for a super-durable 9-inch casting that could take the punishment of both NASCAR circle track and NHRA drag racing. The "N" stands for "nodular iron" case, indicating the solid iron material used. At a glance, the "N" is the quickest way to identify the nodular-iron 9-inch case. But, not all "N" cases received the "N" marking in the casting. Look for the C2AW-A, C4AW-B, and D0OW-B casting numbers when the "N" is missing. Another strong clue for the "N" case is 31-spline axle hubs and shafts. But, finding 31-spline hubs and shafts does not always mean you've found an "N" case. This is why your homework must be thorough. All of the elements of an "N" case must add up.
Another clue with "N" cases is the front pinion support. Like the "N" case, with its high nodular-iron content, the front pinion support was also specific. This pinion support was called the Daytona pinion support. They have the same outer pinion bearing as all 9-inch differentials. They get meaty inside, with a larger inner pinion bearing. There is also a lot more iron inside to support that larger inner bearing. Look for C5AW-C, D1OW-C, and D2OW-C casting numbers. Some have the cast-in guard. Some don't.
If you're out there searching among the ruins and happen to find a 9-inch differential sporting a 9 3/8-inch ring gear, don't be surprised. The 9 3/8-inch case looks more like the "WAR" case mentioned earlier. It has two 12/6 o'clock ribs, like the "WAR" case. It also has a different pinion support, with a C8AW-B casting number. None of these castings are interchangeable with the single-rib or "WAR" cases. And, truthfully, this is a differential to stay away from.