The simplest way to identify the rear axle assembly of a Ford vehicle is to look at the plate stamped on the component. The plate provides important information about the axle assembly, its date of manufacture and the location responsible for creating the part.
Modern Ford differential tags feature the axle assembly model number directly at the top of the tag. A plant code, either S for Sterling or V for Van Dyke, precedes the number. The rounded gear ratio appears in the lower left-hand corner of the tag, and it features an L for vehicles with a limited-slip differential. The number directly next to the rounded number is the decimal position for the ratio, so 3 27 becomes a ratio of 3.27. The code on the bottom right-hand side of the tag identifies the date of manufacture, beginning with the last digit of the year and with letters representing the corresponding month, starting with A for January and progressing through L for December. The last two digits of this code identify the exact day.
Vehicles without a differential tag require visual identification of the assembly. On modern vehicles, 2WD vehicles have only one differential, and 4WD vehicles have two visible on the assembly. A set of 10 bolts on the cover identifies an 8.8-inch differential, and a set of 12 identifies a 9.75-inch differential. A mechanic can use this information, along with the make and model of the vehicle, to determine the correct model number.