How Car Brakes Work (+ 5 Signs of Brake Problems)

Here’s something to think about the next time you’re driving:
Moving at 60 mph, a car needs approximately the length of a football field to stop completely.

Imagine how much longer it’d take if your brakes weren’t in prime condition.

With that said, what makes up a vehicle brake system?
Vehicle brakes come in many forms. Passenger cars usually have hydraulic brakes. Large carriers like trucks may have an air brake system. EVs employ regenerative braking.

However, we’ll be tackling the hydraulic brake system, the one most people think of when talking about brakes.

Let’s grab a wrench.

What Do Car Brakes Do?

Vehicle brakes use leverage, hydraulic force, and friction to stop your car.

Leverage happens when you press the brake pedal. This actuates the master cylinder, which delivers hydraulic pressure to the braking mechanism at the wheels. Friction applied at the wheels converts kinetic energy (from the wheel’s motion) to heat, which dissipates into the air gradually. This is why your brakes get hot.

Fun fact: Brake pads can reach temperatures over 950^oF!

But brakes aren’t just a bunch of discs at your wheels.
There are tons of interconnected brake parts.

Let’s see what these parts are and how they relate.

What Makes Up a Hydraulic Brake System?

We’ll go through the primary parts of a car braking system as each one triggers the next:

1. Brake Pedal: Creates Leverage

The brake pedal is usually the pedal on the left side (of a 2-pedal automatic car) or the middle pedal (of a 3-pedal manual vehicle).

Hydraulic braking begins when you depress the brake pedal. Brake control comes from the pedal; a harder press means harder braking and softer braking comes from gentler brake control.

As the brake light switch is also connected to the pedal, pressing it turns on the brake lights.

While the brake pedal rarely causes issues on its own, it often reflects problems in the braking system.

2. Brake Booster: Amplifies Your Foot Power

Braking takes a lot of force.
Think about it — you’re using just your foot to stop a 2-ton vehicle. That’s where the brake booster comes in.

This ingenious device amplifies your foot power from the brake pedal. The booster uses the vacuum from the intake manifold and differences in air pressure to punch much more force into the master cylinder.

If you have a bad brake booster, your pedal may feel super stiff.

3. Master Cylinder: Converts Force to Hydraulic Pressure

The master cylinder converts kinetic energy from the brake booster into hydraulic pressure.

Here’s what happens:
Brake fluid fills the master cylinder (from the brake fluid reservoir).
Force from the brake booster pushes the master cylinder piston, which “compresses” the brake fluid through the brake lines.

As liquid isn’t compressible, pressure builds and is communicated to the braking mechanism at the wheels.

The master cylinder usually has 2 cylinders (a tandem design) controlling 2 separate hydraulic circuits — each handling 2 of your 4 wheels. This is a safety measure in case one hydraulic circuit fails.

If the master cylinder fails, you may notice a brake fluid leak or your car drifting to one side while braking (from a failed hydraulic circuit).

4. Brake Lines and Brake Hoses: Transfers Hydraulic Pressure

Brake lines and hoses form conduits from the master cylinder to the braking mechanism at the wheels. They carry brake fluid and communicate hydraulic pressure to your disc or drum brakes.

So, how are a brake line and brake hose different?
A brake line is a rigid metal tubing running along the chassis.
A brake hose is a flexible tubing connecting the rigid brake line to the braking mechanism, where there’s wheel movement.

Damage to brake lines or hoses typically results in brake fluid leaks or uneven pressure to wheels — causing the car to pull to one side when braking.

5. Disc Brakes and Drum Brakes: Create Friction at the Wheels

Disc and drum brakes are parts of the brake system that interact with the wheels. Disc brakes create friction by squeezing, and drum brakes do so by pushing. We’ll cover them in detail in the following sections.

How Do Disc Brakes Work?

A disc brake has a caliper, brake pads, and brake rotor.

Pressing the brake pedal creates pressure through the brake fluid, engaging the caliper pistons. This causes the brake pads to squeeze the spinning rotor. Friction between the brake pads and rotor stops the wheel.

Disc brakes have an open design, allowing them to dissipate heat efficiently. You’ll find them on all 4 wheels of your vehicle, or at least on the front 2 wheels when in a disc/drum brake combo. Front wheels take up around 75% of the braking force. So, disc brakes are preferably mounted in front because they can handle more heat and have a faster braking response compared to drum brakes.

Here are the primary disc brake parts:

1. Brake Rotor: Spins With the Tires

The brake rotor (or brake disc) is mounted to the wheel and spins with it.

Brake rotors are typically steel, cast iron, or carbon-ceramic and have different drilled or slotted designs to help with heat dissipation.

Over time, the rotor surface will wear down from contact with brake pads. As its thickness is a significant performance and safety factor, always consider changing the rotor during a routine brake pad change.

Some issues associated with damaged rotors include grinding noise or vibration from warping.

2. Brake Caliper: Squeezes Brake Pads Onto Rotor

The brake caliper is mounted over the brake rotor, has pistons, and holds brake pads on either side of the rotor. Brake calipers typically have one of two designs — a floating caliper (pistons on one side) or a fixed caliper (pistons on both sides).

Faulty brake calipers can leak brake fluid from caliper seals or cause your car to drift to one side.

3. Brake Pads: Stops the Rotor

Brake pads are mounted on the brake calipers, with their friction material facing the rotor. They offer varying levels of stopping power, longevity, and brake dust generation.

As the friction material wears down with use, worn pads shouldn’t be less than 1/4 inch thick before you get new brake pads. Squealing or harsh grinding noises are often a sign of worn brake pads.

Next, let’s take a closer look at drum brakes.

How Do Drum Brakes Work?

Drum brakes are an older brake type with an enclosed design. They comprise a brake drum that encloses a wheel cylinder and brake shoes.

When you engage the brake pedal, brake fluid pressure actuates the wheel cylinder, pushing a pair of brake shoes apart onto the insides of the spinning brake drum. Friction between the brake shoes and drum halts the tires.

Drum brakes are more complex than disc brakes but cheaper to replace. So, you’ll still find them on economy models or as rear brakes where less braking force is needed. It’s also easier to install parking brakes in them.

However, their closed configuration means they overheat faster than disc brakes and tend to experience brake fade more.

Note: The parking brake is a separate device that bypasses your hydraulic brakes. It typically employs the rear brakes, using only cables and levers. The parking brake keeps your car stationary, so it doesn’t move or roll off a slope.

Here are the main drum brake pieces:

1. Brake Drum: Rotates With the Wheel

The brake drum is affixed to the wheel hub and rotates with it. It’s typically made of iron, making it quite resistant to wear.

Brake drums are subject to water ingress, as the water has nowhere to go until enough heat evaporates it. Water between the drum and brake shoes can adversely affect brake performance. Other drum issues include “long pedal” or excessive drum wear, causing wheel cylinder pistons to slip out of their bore.

2. Wheel Cylinder: Pushes the Brake Shoes Onto Brake Drum

The wheel cylinder is inside the brake drum, mounted to the top of the backing plate. It usually has 2 pistons attached to brake shoes and pushes them outwards in response to braking pressure.

A faulty wheel cylinder can leak brake fluid from its seals, and corrosion can jam its piston.

3. Brake Shoes: Stops the Brake Drum

The brake shoe is a curved metal piece with a friction lining on one side. Brake shoe pairs are mounted inside the brake drum, with the friction material facing outwards towards the brake drum’s inner surface. Like brake pads, brake shoe materials come in various options, too.

Worn brake shoes can result in grinding noises or rattling sounds and a less effective parking brake.

Brakes are a crucial element in your car, and plenty of jargon surrounds them.
Let’s go over some, next.

What Are Some Common Brake Terms?

These are some common terms you might encounter when looking up brakes:

Peak Force defines the maximum decelerating effect that brakes can produce. When peak force exceeds the tires’ traction limit, the car starts skidding. It’s kind of like emergency stopping when you’re running — that’s peak force you’re feeling in your legs.

Brake Fade is the temporary loss of braking power when brake heat accumulates and doesn’t have time to dissipate. Large vehicles with heavy loads are more prone to this.

Brake Hydraulics refers to the use of liquid force (i.e. brake fluid) in your braking system. Keeping air out of a hydraulic system is essential as liquid isn’t compressible, but air is.

Brake Bleeding is a brake service that removes air bubbles from the brake lines — usually done whenever brake components are changed.

Brake Pedal Feel describes how brake pedal travel is perceived to affect braking output performance. For example, do you need to tap the brakes only a bit to stop?

Brake Drag indicates how much the brake pad drags against the rotor when the brakes aren’t engaged and is often the result of worn hardware.

Brake Noise encompasses any squeals and grinding when the brakes are applied, typically when brakes are past their prime. Ideally, brakes convert kinetic energy to heat, but sometimes, some are converted to acoustic energy instead.

Brake Smoothness describes how smoothly the brakes perform to a stop. Some brakes can pulse or exert varying brake forces that can lead to skidding.

Next are some indicators that a brake inspection is due.

5 Signs You May Need a Brake Job

Bad brake symptoms can be similar for different brake issues.
Here’s a lineup of 5 usual suspects, and sometimes they come together:

1. Odd Sounds

A high-pitch squealing often means worn brake pads that demand replacement. This is one of the more common issues.

On the other hand, grinding rattling noises may indicate anything from damaged brake pads dragging against a rotor, or rotor corrosion, to broken brake pieces rolling in a brake drum. Could even be a wheel cylinder piston that fell out of its bore.

Now, that’s really bad news, as you’ll be leaking brake fluid and losing hydraulic pressure.

2. Irregular Pedal Behavior

Take note whenever your brake pedal acts differently than usual:

A soft, mushy pedal or a long pedal (one that travels further to brake) can mean anything from a brake fluid leak or air bubbles in the brake line, to worn pads, even excessive brake drum expansion.

A hard, stiff pedal or one that rides high may indicate brake booster issues or extreme brake fluid contamination.

3. Pulling To One Side

If your car feels like it drifts to one side, it can be from a:

Stuck caliper or wheel cylinder piston
Collapsed brake hose or brake line
Unevenly worn brake pads
Master cylinder circuit failure

However, drifting might not even be a brake problem.
Unevenly inflated tires (possibly a punctured tire) or poor wheel alignment can also be culprits.

4. Vibrations

Vibrations often come from warped rotors as uneven surfaces thrum against the brake pads. However, misaligned wheels can cause it too.

You may also experience this if doing an emergency stop with a vehicle fitted with ABS — which isn’t a brake problem. It’s just the ABS making quick grabs on the rotor to stop the car safely.

5. Brake Warning Light Flashes

A lit brake warning light covers a series of errors, from low brake fluid levels or ABS issues, to a still-engaged parking brake. Don’t ignore this light if it pops on.

If your vehicle displays these signs, you should get a brake service ASAP.
Your road safety is worth much more than a brake repair or new brakes.

How Much Does a Brake Repair Cost?

There’s no hard answer to this question.
Replacing “brakes” typically refers to replacing your brake pads or shoes. This can cost anywhere between $200-$1000 (or more), depending on your vehicle’s make and model, location, and brake parts used.

Just keep in mind that a brake repair can involve more than just replacing brake parts.

Safeguard Peak Performance in Your Brakes

Good driving practices include keeping sufficient braking distance and applying gentle pressure on your brakes. Minimizing rash brake use can help improve fuel economy and prevent unnecessary wear to brake components.

Also, remember that periodic brake inspection and regular brake service can help you plan brake repairs and spread out the cost.

For a simple solution to brake repair, you can always count on AutoNation Mobile Service.
We’re a mobile vehicle repair and maintenance service, available seven days a week.