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Axle tubes are components used on a solid-drive axle to house the axles that run from the gear set to the wheel flange. Commonly found on rear-wheel drive automobiles, front and rear axles on some four-wheel drive vehicles and the drive axles of large trucks, axle tubes are used to not only protect the axles, but to also house the axle lubricant. Most axle tubes are welded to the center section of the axle, however, these tubes can often be replaced in the event one becomes bent. Another function of the axle tube is to house the outer wheel bearing in what is commonly referred to as a wheel bearing cup.
Made of steel, the axle tubes are very strong and are used to position and maintain the axle under a vehicle. The axle tube is inserted into the side of the center section of the rear axle housing and welded in place both on the outside of the housing as well as on the inside of the housing. This creates a very strong connection and also seals the axle tubes against leaking gear and axle lube out of the welded connection. The bearing cup is placed against the outside end of the tube and welded into place. This procedure is repeated on the opposite side of the axle housing as well to complete the housing assembly.
Once assembly of the axle housing is complete, the housing is placed in a jig and checked for straightness. Any straightening required is accomplished through a process of heating the axle tube and cooling it, which will correct the bend. This is also the same procedure used to straighten slightly bent axle housings, which are often the result of minor collisions. For more drastically-bent axle tubes, the original tube is cut free with an acetylene torch and a new axle tube is welded into position.
The axle tubes provide the mounting position for coil and leaf-spring mounting points and high-performance ladder bar and four-link suspension mounting points. In circle track racing axle tubes, inner seals are often placed inside the right side axle tube to aid in keeping the gear lube from being forced out of the tube during high-speed cornering. The typical vehicle's axle tubes are made of a mild steel, while high-performance applications are commonly made of a chrominum-molybdenum, or chromoly, steel for a lightweight and extremely strong axle housing assembly.