Axle

Axle is a steel shaft on which the locomotive wheels are mounted. The axle not only holds the wheels to gauge, but also transmits the load from the axle-boxes to the wheels. In some cases the axle is fixed in position with a bearing inside the hole in the wheel or gear to allow the wheel or gear to rotate around the axle. In other cases the wheel or gear may be fixed to the axle, with bearings provided at the mounting points where the axle is supported.

Automobiles and other vehicles usually have a split axle, either front or rear. Each driven wheel is attached to a separate shaft, with a differential and universal joints between the two shafts and providing means to transfer power to the two half axles. The differential and split axle allows the two wheels to rotate at different speeds when the vehicle is turning.

Types
There are several types of axle:

Transaxle - The most common type, which encases an automatic or manual transmission and a differential. The main purpose is the gear changing capabilities of a transmission. Drive Axle - Also called live axle, which contains the differentials. It provides the torque transfer capabilities of a differential. Straight Axle - A straight beam that connects the wheels together, but has no differentials. It helps to support the weight of the vehicle and serves as an attachment point for the wheels.

Maintenance
Axle maintenance is related to the complexity of the axle. A straight axle requires periodic cleaning. Drive axles should have the axle lube level checked with every oil change. Positive lock differentials require a different lube. In cold weather synthetic lubes should be used because they flow easier in this weather. Axle lube is specially formulated oil that is capable of handling high-pressure loads. The lubricants come in various viscosities to meet different specifications. Axle lube provides lubrication for the various gears and bearings in the rear axle of rear-wheel-drive cars and trucks.