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.
For servicing the rear axle, the third letter must be known, which is the manufacturers identity. 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. The rear axle identification number must known to order the exact replacement parts.
On all late model axle assemblies, the axle ratios are designed to meet emission standards for areas of operation. Due to the wide variety of axle ratios available since 1968 it is not possible to list each gear code and ratio number. Depending on the performance options on your vehicle the ratios start at, 2.29 and go as high as 4.88 (early production models) and 2.41-3.42 (later production models). If the identification tag is missing, or it does not have the gear ratio stamped on it, a quick way to determine the axle ratio is to:
- Raise and safely support the rear of the vehicle on jack stands.
- Mark the inside of the wheel with chalk or other suitable marker.
- Mark the pinion yoke at the housing.
- With transmission in neutral, turn the driveshaft (or pinion) and count the number of turns it takes to turn the wheel one complete revolution.
- Lower vehicle.
You now have an estimated axle ratio, examples being; 2 1 / 2 turns of the pinion to 1 turn of the wheel equals about a 2.50 ratio. 3 1 / 4 turns of the pinion to 1 turn of the wheel equals about a 3.25 etc. Remember this is just an estimated ratio and the actual ratio may be slightly different upon ordering replacement parts.