GM Firebird 1967-1981 Repair Guide

Determining Axle Ratio


Many different axle ratios are available in your Firebird. However, not all ratios are available with each axle. If you are contemplating a change of axle ratios, your dealer can advise you as to what gears are available for your axle.

An axle ratio is obtained by dividing the number of teeth on the drive pinion gear into the number of teeth on the ring gear. For instance, on a 3.08:1 ratio, the driveshaft will turn 3.08 times for every one turn of the rear wheel.

The most accurate way to determine axle ratio is to drain the differential, remove the cover, and count the number of teeth on the ring and pinion gears.

An easier method is to raise and support the car safely on jackstands so that both rear wheels are off the ground. Make a chalk mark on the rear wheel and the driveshaft. Block the front wheels and put the transmission in Neutral. Turn the rear wheel one complete revolution and count the number of turns made by the driveshaft. The number of driveshaft rotations is the axle ratio. You can get more accuracy by going more than one tire rotation and dividing the resulting number of driveshaft revolutions by the number of tire rotations.