The Ford 9-inch differential is a popular vehicle rear end noted for its strength and versatility. Many custom vehicle builders and auto restorers use the Ford 9-inch differential as a replacement, even if the vehicle is not a Ford product. The strength of the housing depends on the variation, making proper identification important when purchasing a used differential, or determining if your vehicle is equipped with a Ford 9-inch differential. The FordMuscle website divides 9-inch housing units into three categories: standard case, war case and "N" case.
Determine if the differential is a Ford 9-inch. Classic Concepts in Ridgecrest, Calif. suggests trying to placing a socket wrench with an extension on one of the axle-side bottom bolts of the differential housing. If the socket cannot be used without hitting the housing, it is a Ford 9-inch. On 8-inch differentials, the extension bar will not hit the housing, allowing for easy bolt extraction. A wrench must be used on the 9-inch housing.
Look at the differential housing. According to FordMuscle, the rear hump on a 9-inch housing, viewed from the rear of the vehicle, is generally round in appearance. This, along with the previous step, provides basic unit identification.
Look for visual clues to determine which version of a 9-inch housing is present. On the axle side of the housing, notice any casting particulars. According to FordMuscle, if there is a ribbed pattern, look for a raised letter "N" in a field between the rectangular ribs; this identifies it as an "N" housing. If the rib pattern is present with no "N," it is a war housing. Those with a less defined rib pattern are standard cases.
Locate the identification tag on the axle side of the housing, if present. If it is, locate the Ford part number. FordMuscle lists standard housing part numbers as C7AE-E, C1AW-4025-C and C4Aw-4025-A, with 4025 being the Ford part number designation for differentials. The prefix portion, C7AE, identifies date of manufacture and original model car installation.
