Comparison to Drum Brakes

advantages and disadvantages. The most important points of interest

are discussed below. One major factor that must be discussed in

automotive brakes, as well as all other brake systems, is the

system's ability to dissipate heat. As discussed previously, the

byproduct of friction is heat. Because most brake systems use this

concept to develop braking force, it is highly desirable for brake

systems to dissipate heat as rapidly and efficiently as possible.

The disk brake assembly, because of its open design, has the ability

to dissipate heat faster than the brake drum. This feature makes the

disk brake assembly less prone to brake fade due to a buildup of

excess heat. The disk assembly also may have additional heat

transfer qualities due to the use of a ventilated rotor. This type

of rotor has builtin air passages between friction surfaces to aid

in cooling.

While the brake drum assembly requires an initial shoetodrum

clearance adjustment and periodic checks, the disk brake assembly is

selfadjusting and maintains proper adjustment at all times. The

disk assembly automatically compensates for lining wear by allowing

the piston in the caliper to move outward, thereby taking up excess

clearance between pads and rotor.

The disk system is fairly simplistic in comparison to the drum

system. Due to this design and its lack of moving parts and springs,

the disk assembly is less likely to malfunction. Overhauling the

disk brake assembly is faster because of its simplistic design. It

also is safer due to the fact that the disk brake assembly is open

and asbestos dust from linings is less apt to be caught in the brake

assembly. Like brake drums, rotors may be machined if excessive

scoring is present. Rotors also are stamped with a minimum thickness

dimension which should not be exceeded. The drum brake assembly

requires that the drum be removed for lining inspection, while some

disk pads have a builtin lining wear indicator that produces an

audible highpitch squeal when linings are worn excessively. This

harsh squeal is a result of the linings wearing to a point, allowing

a metal indicator to rub against the rotor as the wheel turns.

Because of its small frictional area and lack of selfenergizing and

servo effect, the disk brake assembly requires the use of an

auxiliary power booster to develop enough hydraulic pressure for

satisfactory braking.

19