Figure 7-13.Self-adjusting mechanisms.
cable then is passed up and over the anchor and attached
to the secondary shoe. Operation is as follows:
1. Brakes are applied and the shoes expand and
contact the drum.
2. The primary shoe self-energizes, and, through
servo action, applies the secondary shoe.
3. The heel of the secondary shoe is lodged against
the anchor pin.
4. The movement of the primary shoe tightens the
cable by shifting the cable guide outward and in the
direction of rotation.
5. The cable then moves the adjusting lever
upward. If enough shoe-to-drum clearance is available,
the adjusting lever will engage the next tooth on the star
wheel. The brake shoes retract and the cable slackens, as
the brakes are released. The return spring then helps
force the adjusting lever downward, rotating the star
wheel, which expands the brake shoes. In the reverse
direction, the toe of the primary shoe is forced against
the anchor, and the secondary shoe moves around to
tighten the adjusting cable. The adjusting process is
Link typeThe link type self-adjusting system
(fig. 7-13) uses solid linkage rods to connect the
adjusting lever to the stationary anchor point. The two
linkage rods, connected together by a bell crank that
pivots on the secondary brake shoe, operate the adjuster.
One rod attaches to the anchor point and the bell crank,