Section 7 (Differential - Positive Traction): Identification
WARNING: This page is about a different car, the 1992 Cadillac Brougham. However, it is still accessible from the selected car via links, so may be relevant.
The differential can be identified as a positive traction unit by raising vehicle and rotating one rear wheel. With transmission in Neutral position, both rear wheels will rotate in same direction if vehicle is equipped with a positive traction differential.
The axle also may be identified by a code stamped on rear of right axle tube 3" (76 mm) from differential housing or backside of right caliper support plate. Brougham models are equipped with an axle code stamped 4MM.