The lining may also be bonded directly to the brake
shoe. In this process, a special bonding agent (glue) is
used to adhere the lining to the brake shoe. After
application, the shoe is baked at a predetermined
temperature to ensure proper setting of the bonding
BRAKE SPRINGS.The brake springs within
the brake drum assembly are the retracting springs and
the hold-down springs. The retracting springs pull the
brake shoes away from the brake drum when the brake
pedal is released. The springs apply pressure to the
brake shoes which push the wheel cylinder pistons
inward. The retracting springs fit in holes in the brake
shoes and around the anchor pin at the top of the
Hold-down springs hold the brake shoes against
the backing plate when the brakes are in a released
position. A hold-down pin fits through the back of the
backing plate, the spring placed over the pin, and a
metal cup locks onto the pins to secure the hold-down
springs to the shoes. Other springs are used on the
adjusting mechanism. Brake springs are high quality,
Figure 7-11.Brake shoes and brake lining.
capable of withstanding the high temperatures
encountered inside the brake drum.
BRAKE DRUMS.The brake drum is attached
to the wheel and provides the rotating surface for the
brake linings to rub against to achieve braking action.
The brake drum is grooved to mate with a lip on the
backing plate that provides the rotating seal to keep
water and dirt from entering the brake assembly.
Brake drums may be made of pressed steel, cast
iron, a combination of the two metals, or aluminum.
Cast-iron drums dissipate the heat generated by
friction faster than steel drums and have a higher
coefficient of friction with any particular brake lining.
However, cast-iron drums of sufficient strength are
heavier than steel drums. To provide lightweight and
sufficient strength, use CENTRIFUSE brake drums
(fig. 7-12). These drums are made of steel with a
cast-iron liner for the braking surface. A solid cast-iron
drum of the same total thickness as the centrifuse drum
would be too weak, while one of sufficient strength
would be too heavy for the average vehicle.