See Figure 1
The axle identification number is located either on a metal tag (attached to the rear of the differential) or stamped onto the front right side of the axle tube, about three inches outboard from the differential cover.
When servicing the rear axle, the third letter of the code must be known in order to determine the identity of the rear axle manufacturer. The codes are: B for Buick, C for Buffalo, G for Chevrolet-Gear and Axle, K or M for GM of Canada, O for Oldsmobile, P for Pontiac and W for Warren.
On late model vehicles, the axle ratios are designed to meet emission standards for areas of operation.