Disc Brake Guide: Parts, Working, and Diagram

What is Disc Brakes?

A disc brake is a type of brake that uses the calipers to squeeze pairs of pads against a disc or a “rotor” to create friction. This action slows the rotation of a shaft, such as a vehicle axle, either to reduce its rotational speed or to hold it stationary. The energy of motion is converted into waste heat which must be dispersed.

Hydraulically actuated disc brakes are the most commonly used form of brake for motor vehicles, but the principles of a disc brake are applicable to almost any rotating shaft. The components include the disc, master cylinder, caliper (which contains cylinder and two brake pads) on both sides of the disc.

This thermal energy generates heat, but since the main components are exposed to the atmosphere, this heat can be diffused efficiently. This heat-dissipating property reduces brake fade, which is the phenomenon where braking performance is influenced by the heat.

Another advantage of disc brakes is their resistance to water fade, which occurs when the water on the brakes significantly reduces braking force. When the vehicle is in motion, the rotor spins at high speeds and this rotational motion discharges the water from the rotors themselves, resulting in stable braking force.

Disc brakes are generally used in passenger cars, but due to their stable performance at higher speeds and resistance to brake fade, they are gradually spreading into the commercial vehicle segment, where drum brakes were traditionally chosen for their longer service life.

Engineering Choice The Biggest Learning Platform

There is increasing demand from customers for longer service life and higher quality, and Akebono is committed to meeting them through further development of the disc brake’s reliability. There are two types of disc brakes.

The “opposed piston type disc brake” has pistons on both sides of the disc rotor, while the “floating type disc brake” has a piston on only one side. Floating caliper-type disc brakes are also called sliding pin-type disc brakes.

Disc Brake Rotor

The brake disc (or rotor) is the rotating part of a wheel’s disc brake assembly, against which the brake pads are applied. The material is typically gray iron, a form of cast iron. The design of the discs varies somewhat.

Some are simply solid, but others are hollowed out with fins or vanes joining together the disc’s two contact surfaces (usually included as part of a casting process). The weight and power of the vehicle determine the need for ventilated discs. The “ventilated” disc design helps to dissipate the generated heat and is commonly used on the more heavily loaded front discs.

Discs for motorcycles, bicycles and many cars often have holes or slots cut through the disc. This is done for better heat dissipation, to aid surface-water dispersal, to reduce noise, to reduce mass, or for marketing cosmetics.

Slotted discs have shallow channels machined into the disc to aid in removing dust and gas. Slotting is the preferred method in most racing environments to remove gas and water and to deglaze brake pads. Some discs are both drilled and slotted.

Slotted discs are generally not used on standard vehicles because they quickly wear down brake pads; however, this removal of material is beneficial to race vehicles since it keeps the pads soft and avoids the vitrification of their surfaces. On the road, drilled or slotted discs still have a positive effect in wet conditions because the holes or slots prevent a film of water from building up between the disc and the pads.

Disc Brake Construction

The brake rotor (disc) which rotates with the wheel, is clamped by brake pads (friction material) fitted to the caliper from both sides with pressure from the piston(s) (pressure mechanism) and decelerates the disc rotation, thereby slowing down and stopping the vehicle.

How Do disc brakes work?

The disc brakes are similar to the brakes on a bicycle. When pressure is applied on the lever, it pulls a metal string that squeezes the two calipers together causing friction between the rubber pads and the metal rim on the tire. Friction between the pads and the disc slows the car down and the disc gets very hot.

When the driver steps on the brake pedal, the power is amplified by the brake booster (servo system) and changed into a hydraulic pressure (oil-pressure) by the master cylinder. The pressure reaches the brakes on the wheels via tubing filled with brake oil (brake fluid).

The delivered pressure pushes the pistons on the brakes of the four wheels. The pistons in turn press the brake pads, which are friction material, against the brake rotors which rotate with the wheels. The pads clamp on the rotors from both sides and decelerate the wheels, thereby slowing down and stopping the vehicle.

disc brake diagram

The main components of a disc brake are:

  • The brake pads
  • The caliper, which contains a piston
  • The rotor, which is mounted to the hub

The disc brake is a lot like the brakes on a bicycle. Bicycle brakes have a caliper, which squeezes the brake pads against the wheel. In a disc brake, the brake pads squeeze the rotor instead of the wheel, and the force is transmitted hydraulically instead of through a cable. Friction between the pads and the disc slows the disc down.

A moving car has a certain amount of kinetic energy, and the brakes have to remove this energy from the car in order to stop it. How do the brakes do this? Each time you stop your car, your brakes convert the kinetic energy to heat generated by the friction between the pads and the disc. Most car disc brakes are vented.

Vented disc brakes have a set of vanes, between the two sides of the disc, that pump air through the disc to provide cooling.

Advantages Of Disc Brakes

There are actually several very important benefits to using disc brakes:

  • Disc brakes offer greater stopping power, which can be helpful on long descents.
  • Disc brakes don’t heat the rim, which has been known to cause tire blowouts on long descents when rim brakes are used.
  • Disc brakes allow for more precise braking, making wheel lockup less likely.
  • Disc brakes work better than rim brakes in wet weather.
  • Changing rotor sizes allows you to adjust how much braking power you want.
  • It’s easier to use wider tires with disc brakes.

Disadvantages of Disc Brakes

  • A disc brake is much more prone to noise so timely service required.
  • The rotors wrap easier than the drum brake system.
  • Disc brakes are not self-energizing thus need higher clamping forces, which requires a power booster.
  • Expensive as compared to a drum brake.
  • Too many components used in this brake so increases weight.