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Disc brakes versus drum brakes

Disc brakes versus drum brakes

Difference between disc brakes versus drum brakes

A disc brake system uses a disc brake pad, caliper and rotor. The disc brake pad consists of a steel backing plate and friction material. In use, hydraulic fluid extends the caliper piston to apply pressure to the brake pads which clamp against the rotor to stop the vehicle. Disc brake systems contain fewer parts than drum brake systems, are self-adjusting and self-retracting, and are more reliable. They do, however, require more braking force to stop the vehicle because they are not servo actuated like drum brakes.

Brake pads

Drum brake, on the other hand, have many more parts, including return springs, links, hold-down springs, and a self adjuster mechanism

drum brake exploded diagram

drum brake

Here’s where things get confusing

Disc brakes were originally used only on the front wheels, which drum brakes in the rear. The reason for retaining drum brake in the rear was to provide emergency/parking brake operation using the brake shoes. Over time, car makers shifted to disc brakes on all four wheels with a cable operated feature on the rear calipers that would apply the brake pads to the rotor when he driver actuated the parking brake. Unfortunately, that combination hydraulic/cable operated caliper was fairly complicated and prone to leaks and early failure. So carmakers abandoned the combination caliper and developed a hybrid disc brake/parking brake system that uses disc brake pads for stopping power with small brake shoes that apply to the rotor hat area for parking brakes.

Rear disc brake with parking brake

A normal caliper applies pressure to the disc brake pads against the brake pad swept area on the rotor. Whent he parking brake is applied, the actuator extends the top of the brake shoes against the swept area shown in the image above. The pressure of the brake shoes against the inner area of the rotor hat serves to lock the rear wheels of the vehicle for parking.
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