GM Full-Size Trucks 1980-1987 Repair Guide

Determining Axle Ratio


Axle ratios available in these trucks range from 2.56:1 to 4.47:1 with nine stops in between. However, not all ratios are available with all axles. If you are contemplating a change of axle ratios, your dealer can advise you as to what gears are available for your particular axle.

Front axle ratios installed on 4-wheel drive models are the same as the rear.

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 4.11 ratio, the driveshaft will turn 4.11 times for every turn of the rear wheel.

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

An easier method is to jack and support the truck 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 result by the number of tire rotations.

The axle ratio is also identified by the axle serial number prefix on the axles. Dana axles usually have a tag under one of the cover bolts, giving either the ratio or the number of pinion/ring gear teeth.