Ford- Fairmount/Zephyr 1978-1983 Repair Guide

Understanding Rear Axles


The rear axle is a special type of transmission that reduces the speed of the drive from the engine and transmission and divides the power to the rear wheels. Power enters the rear axle from the driveshaft via the companion flange. The flange is mounted on the drive pinion shaft. The drive pinion shaft and gear which carry the power into the differential turn at engine speed. The gear on the end of the pinion shaft drives a large ring gear, the axis of rotation of which is 90° away from that of the pinion. The pinion and gear reduce the speed and multiply the power by the gear ratio of the axle, and change the direction of rotation to turn the axle shafts which drive both wheels. The rear axle gear ratio is found by dividing the number of pinion gear teeth into the number of ring gear teeth.

The ring gear drives the differential case. The case provides the two mounting points for the ends of a pinion shaft on which are mounted two pinion gears. The pinion gears drive the two side gears, one of which is located on the inner end of each axle shaft.

By driving the axle shafts through this arrangement, the differential allows the outer drive wheel to turn faster than the inner drive wheel in a turn.

The main drive pinion and the side bearings, which bear the weight of the differential case, are shimmed to provide proper bearing preload, and to position the pinion and ring gears properly.

The proper adjustment of a relationship of the ring and pinion gears is critical. It should be attempted only by those with extensive equipment and experience.

The rear wheels are connected to the differential assembly by axle shafts. The axle shafts are supported in the rear axle housing by bearings and are retained in the housing by bearing retainer plates which bolt to the rear brake mounting plates.

The differential assembly is mounted on two tapered bearings. These bearings are retained in the axle housing by removable bearing caps.

The drive pinion is mounted in the axle on two roller bearings.

An identification tag is attached to one of the inspection plate attaching bolts. The information on this tag must be used when ordering replacement parts.

Axles WER, WGX and WGZ have "C" locks, refer to the 7 1 / 2 " Ring Gear Axle for removal instructions.