Rear end codes, or rear differential codes, vary among manufacturers. Identify General Motors, Ford and Dana Spicer codes using resources from Differentials.com and Dana.com. For other manufacturers, check the VIN at a dealership, or use a combination of mechanical and visual identifiers to determine which differential is in a vehicle.
Dana Spicer rear ends are used on Ford, GM and Chrysler vehicles, and the company provides more information in its codes than any of the axle manufacturers. On a Dana Spicer axle, there is a metal tag attached to the cover of the rear differential and an etching on the housing itself with a six-digit code; the code starts with either a "6" or "2." Entering that code into the BOM identifier at Dana.com returns the rear end in question with gear ratio and differential type.
Ford axles use a similar metal tag on the axle itself that identifies gear ratio, differential type and manufacturing information, according to Differentials.com. There are not identifiable codes on axles manufactured by GM, but in a GM vehicle (regardless of the manufacturer of the rear end), the RPO codes in the glove box beginning with the letter "G" identify gear ratio and differential type.
Differentials.com provides visual identifiers for rear ends by differential cover. Many look identical but still have significant mechanical differences. Similarly, codes on rear ends manufactured by Toyota, Chrysler and others do not have reliable identification methods except through dealerships.