ABSTRACT
Figure 21.1 shows a drum brake as used on a large vehicle. This cut-away view shows that the linings on the shoes are pressed into contact with the inside of the drum by the action of the cam. In this case the cam is partially rotated by the action of a compressed air cylinder. The road wheel is attached to the brake drum by means of the wheel studs and nuts. A brake of this type has a leading shoe and a trailing
shoe. The leading shoe is the one whose leading edge comes into contact with the drum first, in the direction of rotation. A leading shoe is more powerful than a trailing shoe and this shows up in the wear pattern, because a leading shoe generally wears more than a trailing shoe owing to the extra work that it does.
