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Car Brake: What is it and How it Works?

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We know that brake slows down car. But, how?!

If a cat jumps out in front of your cruising car, what do you do?

You brake!

Unless you hate cats. (But you should brake anyway.)

By stepping on your brake pedal, your car magically comes to a halt.

If you’ve ever wondered how that happens, you’ve come to the right place. We’ve jam packed the four most commonly found car brakes into a single post just for you.

What is car braking system?

Here’s a Physics 101 for the day.

Isaac Newton’s First Law of Motion states that “A body at rest will remain at rest, and a body in motion will remain in motion unless acted upon by an external force”.

That means that by the law of physics, a moving car will keep moving forward unless something is there to stop it.

That “something” is a car braking system.

This is a car brake system on Hudson 1937. It hasn't changed much since! The full version image is uploaded by Alden Jewell.
This is a car brake system on Hudson 1937. It hasn’t changed much since!
Full version of the image is uploaded by Alden Jewell.

Car braking system allow drivers to selectively introduce friction upon our car to reduce its speed.

When we step on the brake pedal, the car braking system sends brake fluid to the braking mechanisms (e.g: disc brake, drum brake) found on each of our car wheels.

The brake fluid activates the braking mechanisms, which generates friction that turn movement (kinetic energy) of our car into heat. Finally, this slows the car down.

So if you really think about it, car braking system is like the commander that commands and controls all four of the braking mechanisms found on our car wheels.

To understand how it all happens, we have to take a look at the components of a car braking system.

Let’s break it down (pun intended).

  • Brake pedal : This is the brake that we step on when we want to slow down the car. It connects to the master cylinder mechanically.
  • Master cylinder : Consists of a piston and return spring.
  • Brake fluid reservoir & brake fluid.
  • Hydraulic braking circuit : This is the brake fluid line. It acts as a pipe system for the brake fluid to flow.
  • Slave cylinder : Slave cylinder is part of the braking mechanisms too, which we will be discussing later. It activates the braking mechanisms to slows the vehicle down.

So how does all of these work together to stop our car?

The journey begins with the master cylinder.

Check out this amazing animated video by Thomas Schwenke about Master Cylinder – How it Works.

Master cylinder is the core of our car braking system. If you know how it works, you know the rest!
  • Our brake pedal is connected mechanically to the piston of master cylinder. When we step on the brake pedal, it depresses the master cylinder’s piston.
  • Inside the master cylinder, the brake fluid gets squeezed into a smaller space, and therefore pressure increases.
  • The pressurized braking fluid then escapes through the fluid line into the slave cylinder at each car wheels
  • Finally, this activates the braking mechanisms which slows our car down.

Most modern cars have two master cylinders running in parallel to each other, just in case if one of them fails. When it comes to safety, we never take chances.

Similarly to how we have power assisted steering rack to steer our car easier, we have power assisted brakes to make braking easier too!

Power assisted brakes work the same way as non-power assisted ones, except it has an additional booster located between the brake pedal and the master cylinder. They can be either vacuum assist or hydraulic assist but that would be another story for another day.

For now, we’ll explore some of the most commonly found braking mechanisms.

Types of Braking Mechanisms

We talked about car braking system earlier, but it doesn’t physically slows down the car. It just activates the braking mechanisms.

The act of slowing down actually happens at the braking mechanisms.

There are many types of braking mechanisms. But the most common ones would be:

1. Disc Brake

Disc brakes are commonly found on the front wheels.
Disc brakes are commonly found on the front wheels.

Disc brake is a type of brake that squeezes brake pads against a disc to reduce our vehicle speed. Hence, the name “disc” brake!

You would usually find disc brakes installed at the front wheels and there is a reason for that.

Front brakes play a greater part in stopping our car – about 65% to 75%, because braking throws the car weight forward.

Being the more effective braking mechanisms, we install disc brakes in front.

Some high end cars like Lamborghini and Porsche also have them at the rear wheels for some crazy off the chart braking power.

What makes up a Disc Brake?

  • Brake disc (rotor) : Made from cast-iron, it attaches to the moving part of the wheel assembly which spins together with the car wheel. They are designed with holes so that air can pass through to cool the brake disc.
  • Calipers : Calipers houses the caliper piston, brake pads, and hydraulic connections.
  • Caliper pistons: When activated, it forces the brake pads onto the brake disc.
  • Brake pads: We find them on both side of the calipers, just 1 mm away from the brake disc. They are the sacrificial frictional lining that will clamp onto the disc when activated. The friction slows the car down.

How Disc Brake Works?

  • Garfield the Cat jumps in front of your cruising car.
  • You slam on the brake pedal.
  • The hydraulic fluid flows through the braking circuit and find its way to the disc brake.
  • This pressurized fluid enters through the calipers and forces the caliper pistons towards the brake pads.
  • Caliper pistons moves the brake pads until it touches the brake disc.
  • The brake pads has frictional lining that clamps onto the brake disc.
  • The clamping motion stops the brake disc from moving.
  • Because brake discs are attached to the car wheels, the car wheel stops rotating when brake disc stops.
  • Your car stops just before hitting Garfield the Cat!

Bartosz Stubiński has made a super clean animated video on Disc Brake 3D Animation and it’s worth a million words. Definitely have a look.

Advantages of Disc Brakes:

  • More effective braking.
  • Minimal maintenance required.
  • Quick and easy to replace.
  • Able to check wear without dismantling it.

Drawbacks of Disc Brakes:

  • We couldn’t integrate a handbrake into it.
  • Brake pads wear out very quickly.
  • Expensive.

2. Drum Brake

Drum brake are usually found at the rear wheels.
Drum brake are usually found at the rear wheels. Image courtesy of Wapcaplet.

Drum brake is a cheaper and more durable form of car braking system. But, it has lesser braking power as compared to the disc brake.

It is the exact opposite of disc brake and therefore complementing it perfectly.

Most of the time, we will only see drum brakes at the rear wheels of our car. It is only responsible for 25 – 35% of braking power.

The working nature of drum brake also makes it easy for engineers to integrate handbrake into this system too. You’ll learn about it in the next section!

What makes up a Drum Brake?

  • Brake drum : A cast iron drum bolted to the wheels.
  • Back plate : A plate that houses the other components of drum brake listed below.
  • Brake shoes & brake lining : Rubs against the inner wall of brake drum to produce friction.
  • Retainer springs : Holds the brake shoes in start position.
  • Wheel cylinder : Pushes the piston outward to move the brake shoes.
  • Brake adjusters : Automatically adjusts brake shoes position to compensate for wear in the brake lining.

How Drum Brake Works?

  1. Garfield the Cat (again?!) jumps in front of your cruising car.
  2. You slam on the brake pedal.
  3. Brake fluid flows from the master cylinder, through the braking circuit and find its way to the drum brake (usually your rear wheels).
  4. This pressurized fluid enters through the wheel cylinders and forces the cylinder pistons to move outwards.
  5. As cylinder pistons moves, it also forces the brake shoes outwards until it touches the inner walls of brake drum.
  6. The brake shoes have frictional lining that presses hard against the inner walls of brake drum.
  7. This generates friction that slows down the brake drum.
  8. Because brake drum is bolted to the car wheels, the car wheel stops rotating when brake drum stops.
  9. You do not run over Garfield the Cat!
crashforensics‘s training video showcases Drum Brakes in a clear and concise manner. Couldn’t have done it better myself.

Advantages of Drum Brakes

  • Durable.
  • Handbrake can be integrated into this braking mechanism.
  • Cheaper.

Disadvantages of Drum Brakes

  • Unable to check brake lining wear unless you dismantle the entire drum brake.
  • Heats up quicker due to the enclosed design.
  • Complicated design.

3. Handbrake

Handbrake lever are found between the driver and front passenger's seat.
Handbrake lever can be found between the driver and front passenger’s seat.

Handbrake is a 100% mechanical braking system that is completely separated from the hydraulic braking circuit.

Unlike disc and drum brake, it doesn’t use any hydraulic to brake.

Instead, it uses good ol’ metallic brake cable and levers to work.

This means that it can be used as an emergency brake should your hydraulic brake stops working.


Well, hopefully we won’t ever need to use it like that.

Although it can be used as an emergency brake, its primary function is to keep your car stationary in parking mode – especially when it’s parked on a slope.

What makes up a Handbrake?

  • Handbrake lever : This is the handbrake that we always pull when we are parked.
  • Metallic cables : High tension metal wiring that connects to the drum brakes.

How Handbrake Works?

  • You pull the handbrake lever.
  • The cables transmit the force to the drum brakes at rear wheels.
  • The metal cables tightens and forces the brake shoes out.
  • Brake shoes presses hard against the inner wall of brake drum.
  • It restricts any movement from the brake drum.
  • Brake drum is now held stationary and therefore your car cannot move.
Handbrake is a simple mechanism but yet so important. Viren Chitroda made a short video on How Handbrake Works that will give you a “A-ha!” moment.

Advantages of Handbrake

  • Can be used as an emergency brake.
  • Prevent your vehicle from rolling away when parked.

Disadvantages of Handbrake

  • Will rusts if you don’t use it (quite unlikely).
  • If you forget to release the handbrake, driving can damage your rear brake very quickly.

4. Anti-lock Brake System (ABS)

ABS sensors are attached to the wheels to monitor wheel speed.
ABS sensors are attached to the wheels to monitor wheel speed. Image courtesy of NSX-Racer.

During panic braking, we slam on the brake pedal hard so that we can stop quicker.

When the braking force is stronger than the traction of the tyre, the tyre will no longer grabs onto the road.

Braking force of this magnitude clamps the car wheels so tight that it stops the wheel from rotating and you start to skid.

We lose steering control and our car start to slide like it’s on ice!

We call this wheel locking and it’s very VERY dangerous.

Anti-lock Braking System (ABS) is an active-safety feature that prevents our car wheels from locking up during emergency braking.

It maintain the braking force at a sweet spot just enough to not have wheel lock while slowing the car down quickly.

What makes up an Anti-lock Braking System (ABS)?

  1. Sensors : Sensors are equipped at all four wheels.
  2. ABS ring : Found on drive shaft / half shaft. It is a circular part with teeth that rotates with the wheels. Sensors reads the teeth to detect the rotation of car wheels.
  3. ABS control module : The brain that makes decision whether or not to allow or block the valve.
  4. Valve : Controls the flow of braking fluid into the braking mechanisms.
  5. Pump : Provides fluid pressure.

How ABS Works?

  1. Sensors monitors wheel speed constantly by reading the ABS rings.
  2. As long as all the four wheels are rotating at similar speed, ABS won’t activate.
  3. Garfield the Cat jumps in front of your car.
  4. You panic brake and slam onto the brake pedal as hard as you can!
  5. Under panic braking, one of the wheels rotates at a significantly different speed compared to the other wheels. This implies that it’s going to lock.
  6. The sensor detects that and reports to the ABS control module.
  7. ABS control module then commands the valve to open up and relief some of the braking fluid back to the master cylinder.
  8. With lesser braking fluid, fluid pressure is lesser and therefore reducing the braking force of the wheel.
  9. Therefore, the wheel does not reach a point of locking.
  10. The process repeats itself in split seconds until the car is slowed down. That is why we will feel pulsation when the ABS is functioning.
A great example of Wheel Locked, Non-ABS Braking in Slow Motion by Craig PP. Do not try this at home.

Advantages of ABS

  1. Helps maintain steering control
  2. Prevents vehicle from skidding during panic braking

Disadvantages of ABS

  1. Higher cost. But as you can see, the safety feature saves life and outweighs the cost. As of 2018, virtually all modern vehicles are already fitted with this.

Symptoms of a Faulty Brake

Our car brake is one of the most important safety feature that we can have in a car.

I wouldn’t drive in a car that has no brakes!

Likewise, we wouldn’t want to drive a car with faulty brakes too.

It is essential that we can identify any early signs of a faulty brake so that we can take immediate action.

Granted that faults in brake will vary depending on their type, here are a few common symptoms of a faulty brake:

  1. Metal screeching sound while braking : This is the most common symptom of faulty brakes. This could be caused by a worn out brake shoes and the metal of the calipers are rubbing directly against the disc or even wrong alignment of calipers and the disc or the drum.

  2. Odd noise even when NOT braking : This could happen when you have a misaligned calipers or dented disc protector that rubs against the disc even without braking. This can very well happen when installing drive shaft.

  3. Leaking brake fluids : Braking fluid rarely needs top up. If you have to top up your braking fluid in less than half a year, chances are you have a leak somewhere on your hydraulic brake circuit.

  4. Car leans to one side while braking : This happens when there is uneven braking. It is usually caused by one side of the car having faulty braking that is not providing the stopping action that it should.

  5. Brake pedal feels spongy and soft when pressed : Faulty actuation systems, i.e., brake pedal is hard to press/goes in too easily could be signs of air within the system, faulty braking or a fluid leak.

If you notice any of these symptoms, maybe it’s time to pay your local mechanic a visit.

The Bottom Line

That sums up everything that you need to know about car brakes.

With these braking mechanisms, we can selectively slows down our car. It makes driving that much safer for both you and I.

So, what do you think?

Have you ever had a faulty brake before? What was it like? And how much did you fix it for?

Leave a comment down below and we will respond to you.

Until then, drive safe and drive smart!

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