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TM 9-8000
is available, the adjusting lever will engage the next tooth
(2) The pivot point of the bell crank is moved in
on the star wheel. The brakeshoes re- tract and the
the direction of rotation.
cable slackens as the brakes are released. The return
spring then helps force the adjusting lever downward,
(3) The lever moves up on the star wheel
which rotates the star wheel and therefore expands the
through the connection of the linkage. If enough
brakeshoes. In the reverse direction, the toe of the
clearance Is available between the brakeshoes and
primary shoe is forced against the anchor and the
drum, the lever will engage an- other tooth on the star
secondary shoe moves around to tighten the adjusting
wheel. As the brakes are released, the shoes retract and
cable. The adjusting process then is completed.
the return spring helps force the adjusting lever down,
therefore rotating the star wheel and expanding the
b. Link Type. The link-type self-adjusting system (B,
adjusting  screw  to  remove  excess  shoe-to-drum
fig. 34-10) uses solid linkage rods to connect the
adjusting lever to the stationary anchor point. The
adjuster is operated by the two linkage rods connected
c. Lever Type. The lever-type self-adjusting system
together by a bell crank, which pivots on the secondary
(C, fig. 34-10) is similar to the link type, In that it operates
brakeshoe. One rod attaches to the anchor point and the
in the reverse direction only. While the link-type system
bell- crank, while the other rod connects the bell crank
uses linkage rods to perform the self-adjusting process,
and the adjusting lever. In this configuration, the self-
the lever type uses a stamped metal lever to engage the
adjuster works only in the reverse direction. As the
star wheel and an actuating link to connect to the anchor
vehicle is backing up and the brakes are applied, the
pin. The adjusting process is the same as the link-type
adjusting process Is as follows:
(1) The secondary shoe moves away from the
anchor because of the self-energizing action.
frictional surface for the rotor to engage during braking.
34-13. General. The disk brake system (fig. 34-11) is
another form of brake system used in many modern
a. Operating Principles. The disk brake, like the
vehicles. Like the drum system, the disk brake system is
drum brake assembly, is operated by pressurized
operated hydraulically and has rotating and nonrotating
hydraulic fluid. The fluid, which is routed to the calipers
components. Disk brakes can be used on all four wheels
through steel lines and flexible high-pressure hoses,
or they can be mounted on the front wheels and used in
develops its pressure in the master cylinder. Once the
conjunction with drum brakes, which are mounted in the
brake pedal is depressed, fluid enters the caliper and
rear. These configurations are very popular because the
begins to force the piston(s) outward. This outward
disk system is a very efficient brake system, it stays cool
movement forces the brake pads against the moving
due to its open design, and is less prone to brake fade.
rotor. Once this point is reached, the braking action
The rotating member is in the form of a heavy round-
begins. The greater the fluid pressure exerted on the
shaped disk. The disk or rotor Is attached to the wheel
piston(s) from the master cylinder, the tighter the brake
assembly and may be a solid or vented construc- tion.
pads will be forced against the rotor. This increase in
The disk may be an Integral part of the hub or
pressure also will cause an increase in braking effect. As
detachable from the hub by the use of bolts. The clamp
the pedal is released, pressure diminishes and the force
assembly or caliper is the stationary member in the
on the brake pads is reduced. This allows the rotor to
system and usually is mounted to the spindle or splash
turn more easily. Some calipers allow the brake pads to
shield to provide support. The caliper is fitted with one or
rub lightly against the rotor at all times in the released
more pistons that are actuated hydraulically by the fluid
position. Another design uses the rolling action of the
pressure developed in the brake system. Brake pads are
designed to fit into the caliper and provide the


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