How disc brakes work

25.03.2019
How disc brakes work

How disc brakes work ➤ Disc brake system ➤ Servicing your brakes ✅

Many modern cars are built with two braking systems – the drum and the disc brakes. The disc brakes are located in the front wheel because that is where most braking pressure is felt.

Most of these cars use the single-piston floating caliper disc brakes. In this guide, we are going to see how this disc brake design works.

Do you know where the disc brake is located in your car? Well, like any braking system, it is on the tires of the vehicle. The disc braking system is the best and most efficient braking system in modern cars. It is integrated with drum braking to make braking easy.

Parts of a disc brake include:-

  • The brake pads
  • The caliper, in which a piston is contained and
  • The rotor mounted on the hub.

The disc brake system offers excellent functionality. It can withstand more heat during high speed braking and it is more functional.

How disc brakes work

If you know how a bicycle brake works, then you already have some clue about disc brakes. The two are a lot similar. In a bike brake for instance, there is a caliper that squeezes the brake pads against the wheel. The more pressure you apply, the faster the wheel slows down and stops.

The disc brake on the other hand has brake pads too that squeeze the rotor instead of the wheel. While bicycle brakes directly squeeze the wheel, the disc brake works indirectly from the wheel.  The force is transmitted through hydraulic system instead of a cable.  The disc slows down as a result of the friction between the pads and the disc.

When a car is moving, it produces kinetic energy. This energy pushed the vehicle forward and must be removed for the vehicle to slow down. The question is how the brakes manage this? When the disc brake working is normal, the kinetic energy is converted into heat which comes from friction between the pads and the disc.

Disc brake system

Most of the disc brake systems have vents. These vented disc brakes are characterized with a set of vents between the sides of the disc. There function is to pump air through the disc, to offer a proper cooling system.  

Self-adjusting features

One of the best features of the floating caliper disc brake is self-centering and self-adjusting. Whenever the brake is applied, the caliper is able to slide from side to side and to the center.

If you observe a disc brake diagram carefully, you will notice there are no springs to pull the pads back away from the disc. This makes the pads to always keep a light contact with the rotor. But there is the piston rubber seal, together with any wobble in the rotor, which may together pull the pads a little far away from the rotor.

The pistons in the rotor are much larger than those in the master cylinder in diameter.  In case the brake pistons retract into the cylinders, it might take a number application on the pedal to get enough fluid into the brake cylinder.  This is the best way to engage the pedal in these brakes.

Self-adjusting disc brake

On older auto, they mostly had dual or four-piston fixed-caliper designs. Each side of the rotor had a piston, or two, which were used to push the pad on either side. This design is no longer applicable on the modern market. In their stead, cheaper and more reliable single-piston design has taken over.

Emergency brakes

Most of the modern cars are made with front-wheel having the disc brakes. The rear wheels are mostly made with drum brakes. This is because of the prices which manufacturers seek to reduce.

There are however some cars that have disc brakes on all four wheels. On such vehicles, the actuation of emergency brakes is achieved by a separate mechanism. It is not through the primary brakes, like the case in most cars where a cable is included. These emergency brakes come up in case of brake failure.

In some of the cars with four-wheel disc brakes, there is a separate drum brake integrated into the wheel hub. This drum brake is only activated in an emergency situation. There is no hydraulics attached to this system.

In other cars, the emergency braking is achieved through a lever that turns a screw. If not a screw, it actuates a cam. In this case, the screw, or the cam presses on the piston of the disc brake.

Servicing your brakes

Now that you understand the disc brake working principle, servicing is another area you need to get well. Many people do not take into consideration serious brake servicing. For them, everything is ok as long as the brakes can stop the car. Here are some of the components to consider:-

  • Disc brake pads. Brake pads are the most common service required for brakes. Changing the pads is simple and straight. The pads are more of less like the motorcycle brake pads. If you can change the cycle brakes, then you can get the ones for your car quite easily.  How do you know when to change? You should here squealing noise when the brake indicator comes in contact with the disc. This should tell you the friction material is worn and you need new pads.
  •  You can also use the inspection opening to determine how much is left of your brake pads. There are sometimes deep scores in the brake rotors. This is normal for worn brake pads that are left to stay too long. The rotors can also warp and lose their flatness. You should feel this through brake vibration when you stop.

You can fix these issues by refinishing/turning/machining the rotors. The material is removed from both sides of the rotors in which case, the flat and smooth surface of the rotors is restored.

However, do not refinish too often. Only do it when the brake shoes are replaced. Refinishing more than necessary will reduce their life.