General Motors differential codes for late model vehicles are identified by the production codes that begin with the letter "G." Production codes are found either in the glove box or door jamb of a GM vehicle and list a large number of codes beginning with letters from A to Z. All "G" codes refer to the differential and give information such as ring and pinion gear ratio and the type of differential installed at the factory.Continue Reading
Older GM vehicles may or may not have production codes readily available. These vehicles include production and casting codes on the rear axle housing and differential that gives some information about the differential. There is not a uniform method to derive information from GM axle casting numbers, but some can be decoded. As of November 2015, TheCamaro.com provides a decoder for GM axles manufactured from 1962 through 1970.
Differential identification sites such as DiffWizard.com also help correctly identify key differential information. Users can input year, make, model and drive type of their vehicle into DiffWizard.com to access a database of differentials that were used on that particular vehicle. Visual identifiers such as cover bolts and shape of the differential cover can then be used to correctly identify which GM differential is beneath the vehicle.Learn more about Transmission