the axle tag is missing, as most are, you need to remove the third member in order to know what ratio you have and if it has a limited-slip or not.
This custom axle tag was obviously hand cut as evidenced by the sharp tin-snipped-looking ends and includes DSO, for Dealer Special Order. Notice that the date code is C9UA with the ring gear size of 8.7. This was an 8.75-inch ring gear in a 9-inch housing. These were used sporadically until about 1969. You can install a true 9-inch gear in these housings as well.
Don’t be surprised if the tag you have does not exactly match this. There are also unique domestic special-option tags, which don’t follow the format.
Date Code
The date code is stamped on the tag. The first number is the last digit of the model year of the decade, the next digit is a letter and represents the month (A is for January, B is for February, and so on), and the last two digits represent the day of the month. This format is also applicable to casting date codes.
The date code on this axle tag is 7AC, and it corresponds to the 7th year, 1st month (January), and 3rd day. The WFE-V2 helps us find the decade of the 1970s. This axle tag belongs to a 1977 F-150.
A metal axle tag is typically located on the driver-side front of the third member. It is underneath one of the nuts that holds the third member in place. In most cases, the tag has been lost. On this particular third member, the original copper washers that were under the factory fasteners have been discarded as well.
Some tags reference the week of the month instead of the exact day and just use a letter (A to E) for first through the fifth week of the month.
Case Type
You are looking for a nodular iron case, with its telltale “N” cast into the front or inside wall. These third members are the strongest of the production cases and the most desired. Aftermarket vendors are actually re-casting these cases in very strong nodular iron, so more often than not it is easiest just to purchase a new case.
But if you’re looking for an original, they can be spotted quite readily even without an axle identification tag. The N cases had two vertical ribs, three horizontal ribs, and a machined-in fill plug. There are four versions of the nodular iron third members that were produced from the factory. These first became available on the 1964 Galaxies with the 427-ci engine and were found on many higher horsepower cars and trucks.
Of the four versions of the N case, three have an actual “N” cast into it right above the pinion cartridge.
The fourth version did not have the “N” in the casting on the outside but still retained the rib structure. In order to verify a nodular unit, you need to look on the inside of the casting. These have a C4AW-4025-B casting part number next to the adjuster nut.
Of course, if your budget allows, you can purchase an aftermarket iron case that is stronger than any factory case. If you are looking for an N case or think that you have found one of these desirable axles, make certain to examine it closely. The WAR, WAA, and WAB cases have the same ribbing as the N case, but are missing the ever important “N” feature.
Any of the W-series cases do have a fill plug machined in them. Both standard and W-series cases are made out of gray cast iron. Only the N-series cases are made out of the stronger, more desirable, nodular iron. While the iron is molten, magnesium is added to increase the shear strength of the alloy. The magnesium addition causes the grain structure to change from flakes to nodules and thus the name “nodular” iron. The N cases typically came with the larger Daytona-style pinion support bearing, and 31-spline axle shafts.
This chart references the connection between the month codes and the actual month. The letters I and O are skipped to avoid confusion with the numbers one and zero.
Pinion Cartridge
There are even different pinion cartridges that have been available from the various production years and models for this axle. The Daytona-style cartridge allows for a larger pinion head bearing when compared to the standard pinion cartridge. This is a great upgrade component to use for high-power applications or if you are replacing your cartridge.
Housing
Like most Ford axles, the 9-inch has a single hypoid ring gear mounting distance, so, unlike the Dana and GM axles that require unique differential carriers based on ratio, a single differential carrier works with all of the Ford ratios. Also, since this axle is used in so many circle-track race cars, the 9-inch enjoys an unparalleled availability of different gear ratios in the aftermarket.
This case looked like a nodular unit from the front regarding rib structure but did not have the “N” on it. When you look on the inside, you see WAB-4025A. This is not a nodular unit.
The desirable N-style, nodular-iron gear cases are available in four different versions. There are three versions with external Ns cast in; note the more curved style on the top right. The unit on the top left seems to be nodular iron but requires a little more investigation to verify.
This is when making a few phone calls to reputable axle builders can be helpful. There are quite a few companies making Ford 9-inch housings to fit just about any muscle car out there, including non-Ford vehicles. (See Chapter 8 for how to install a 9-inch in a classic 1957 Chevy Bel Air as a performance upgrade.)
The aftermarket Daytona-style pinion cartridge accommodates the larger and stronger pinion head bearing. This particular pinion cartridge is well reinforced and much stronger than the stock production cartridge.
Here are the internal sides of the same three units. Now
