The components of commonly used final drive units are
shown in Figure 38-22.There are several other basic design
arrangements. However the most commonly used
design has pinion/ring gears and a pinion shaft. The latter
is normally a spiral bevel gear mounted on an input
(pinion) shaft. The shaft is mounted in the front end of
the carrier and supported by two or three bearings. An
overhung pinion gear is supported by two tapered
bearings spaced far enough apart to provide the needed
leverage to rotate the ring gear and drive axles. A straddle mounted
pinion gear rests on three bearings: two tapered
bearings on the front support the input shaft and one
roller bearing is fitted over a short shaft extending from
the rear end of the pinion gear.
The pinion gear meshes with a ring gear. The ring
gear is a ring of hardened steel with curved teeth on one