If your car was built in the last 30 years it is more likely to have brake pads and discs, rather than drums, on either all 4 wheels or at least the front 2. Today almost all mid-range vehicles use brake pads and discs, but why? What is the difference between pads and discs and the previously used drums?
After hand levers, brake drums are one of the earlier automotive braking systems. They are called drums because the components are housed in a round drum that rotates, along with the wheel.
How they work:
Inside the drum is a set of shoes that, when the brake pedal is pressed, are forced to expand against the walls of the drum, creating friction and slow the wheel.
Brake fluid is used to transfer the movement from the brake pedal to the movement of the brake shoes. The shoes are made from heat resistant material, similar to clutch plates.
Brake pads and discs:
Brake discs rely on the same principle to slow a vehicle as drums do (heat and friction), but the movement is different. Instead of having the break shoes expanding outwards to the walls of the drum, when the break pedal is pushed the break pads will clamp together, squeezing the disc to slow the vehicle.
Unlike brake drums, brake discs use a slim rotor and small caliper, which are exposed to the air, to slow wheel movement. As the components are exposed to air it allows for constant cooling to the disc, reducing the chances of overheating or warping.
How they work:
Within the caliper there are two brake pads on either side of the disc, these clamp together using brake fluid as their force when the brake pedal is pushed.
Brake drums, pads and discs ultimately do the same job using the same principles (friction and heat), just in slightly different ways.
From how they are built brake discs are the safer option due to their ability to disperse heat more effectively than brake drums can. This means there is less chance of the brakes overheating and fading which can become dangerous.
Brake pads and discs are safer as they can be inspected without removing the wheel unlike brake drums, this makes it easier to identify when maintenance is needed.