When it comes to vehicle safety, brakes are one of the most crucial features. Among the different types of brakes, disc brakes have proven to be a popular choice due to their ability to provide effective and consistent braking. If you want to know what is a disc brake, let us take a look at what disc brakes are and how they work.
What is Disc Brake?
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.
How Do disc brakes work?
Brake rotors of disc brakes rotate with the wheels, and brake pads, which are fitted to the brake calipers, clamp on these rotors to stop or decelerate the wheels. The brake pads pushing against the rotors generate friction, which transforms kinetic energy into a thermal energy.
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
Check out the diagram; it shows the disc brake layout with a floating caliper, which is the most common design in modern cars. The brake disc or ‘rotor’ (the green part) is installed on the hub. The wheel (not shown here) is installed on the same hub. The brake disc rotates together with the wheel.
Disc Brake Parts
The disc braking system involves many different components, but at its most basic function, the system consists of a disc/rotor, a brake calliper and brake pads. When the brake pedal is applied, brake fluid creates pressure and squeezes the brake pad against the rotor and creates friction. This friction slows the rotation of the wheels and the car itself. Simple?
There is obviously a little more to it than that, with each component engineered to maximise breaking performance.
#1. DISC/ROTOR.
The disc or rotor is the largest part of the disc brake system and is fixed to each wheel, via the holes on the front of the hub (pictured). Discs usually consist of cast iron, but each will have a specific mix of metals based on the vehicle type and performance needs. The disc is the contact surface for the generation of friction in the braking system, so it needs to be able to withstand immense pressure and heat.
Due to the intense heat applied to the disc during the process, the majority are ventilated, optimizing the flow of cold air during braking. This stops the disc from becoming too hot, potentially damaging the disc or other parts of the system.
The vent design is specific to the car manufacturers request and can take upon a variety of different shapes and types. Another method used to increase air flow, is to machine grooves on the exterior of the disc. Much like the vents, these increase surface area and optimize air flow to the disc and the braking surface directly.
#2. BRAKE CALIPER.
Brake calipers are the clamp like component that fits over the disc. Their main function is to push the brake pads into the disc, and they do this via pistons and hydraulic brake fluid.
Inside the calipers are pistons, which have the brake pads attached to them. When we put our foot on the brake, pressurised fluid is sent to the pistons and they push against the pads, which contacts with the disc surface.
#3. BRAKE PADS
The final primary component of the brake disc system is the brake pad – the pad is a steel backed plate, with a friction-based material bound to their surface. Usually there will be two housed within the brake caliper, attached to the pistons with the friction surface directed at the disc.
Sufficient friction material on the pad is essential, as the disc may become damaged and worn down without the correct contact during the braking process. Brake pads can come in a variety of different materials, dependant on the type of cars needed to be stopped.
In order to stop a vehicle weighing in excess of 1000kg, the pads need to be able to withstand extreme heat and friction. Surprisingly there is a large variety of different materials used for brake pads, all considerably resistant. The most popular material and likely to be on your own car, is a metallic brake pad. They’re a blend of different metals; commonly made of iron, copper, steel and graphite.
Metallic brake pads are heavy though and if speed is the name of the game, then a more lightweight material is needed, such as ceramic. You can read more about the different brake pad types and materials here.
#4. BRAKE HARDWARE.
Aside from the four main brakes components, your brake system contains a few smaller parts. If you’re lucky, your braking problems stems from one of these little guys, which would mean a quick, easy, and affordable fix:
- Caliper Pins: Most brake calipers contain two pins which help to move the caliper as pressure is applied to the brake pads. Sometimes the pins corrode, which can prevent them from doing their job effectively, and creates uneven wear and early failure of brake pads. Pull the pins and replace contaminated grease to allow them to move freely again. If they are too damaged, replace with new pins.
- Caliper Pin Boots:The pins mentioned above are installed inside of these rubber boots that allow for movement with protection from the weather and road debris. If torn, they lose their ability to do their job and can cause allow damage to happen in a hurry. Replace all torn or dry rotted boots to keep your system clean and closed.
- Abutment Clips: Abutment clips are the stainless pieces that the pads slide on within the caliper bracket. You should replace these clips with every brake job, as they are spring loaded and lose their tension and ability to aid the pads over time. We now include these clips in all of our Duralast Gold brake pad boxes.
Two Types of Disc Brakes: Floating & Fixed
There are two types of disc brakes. They are floating and fixed, named for the type of brake caliper used.
A floating caliper (also called sliding) is the most common type. It has one or two pistons. When the brakes are applied, the inner brake pad is forced against the disc while, at the same time, the caliper body moves closer to the rotor. This action forces the outer brake pad against the rotor.
The fixed caliper design has one or more pistons mounted on each side of the rotor. The caliper itself doesn’t budge or move. It’s rigidly fastened to a brake caliper bracket or spindle. When the brakes are applied, only the caliper pistons move, pressing the brake pads against the disc.
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 is required.
- The rotors wrap easier than the drum brake system.
- Disc brakes are not self-energizing and 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.