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.
Cars have more than one way to brake — typically hydraulic brakes, engine braking, and parking brakes.
However, in this article, we’ll be tackling the hydraulic brake system, the one most people think of when talking about brakes.
This Article Contains:
- What Do Car Brakes Do?
- What Are The Components Of A Brake System?
- Understanding Disc Brakes
- Understanding Drum Brakes
- 5 Signs You May Need A Brake Job
- 4 FAQs On Brakes
Let’s dive right in!
What Do Car Brakes Do?
Vehicle brakes use leverage, hydraulic force, and friction to stop your car.
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 950oF!
But brakes aren’t just a bunch of discs at your wheels.
There are tons of brake parts that are interconnected.
Let’s see what these parts are and how they relate.
What Are The Components Of A 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 car).
Hydraulic braking begins when you press the brake pedal, triggering a sequence of events that lead to action at the wheels. The brake light switch is also connected to the brake pedal, so 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.
Here are some examples:
- A spongy pedal can indicate air in the brake lines or a brake fluid leak
- A vibrating pedal can imply warped rotors
2. Brake Booster: Amplifies Your Foot Power
Braking takes a lot of force.
Think about it — you’re using just one 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. It does so using the vacuum from the intake manifold and differences in air pressure, resulting in much more force punching into the master cylinder.
If you have a bad brake booster:
- Braking distance increases
- The brake pedal feels super stiff, like squishing a pile of bricks
- A hissing noise may imply a booster leak
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 that “compresses” the brake fluid through the brake lines.
As liquid isn’t actually 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, here’s what can happen:
- A brake fluid leak can form under the front of the car where the master cylinder is
- The brake pedal won’t spring back smoothly into position
- The car drifts to one side while braking if one hydraulic circuit fails
4. Brake Lines And Brake Hoses: Transfers Hydraulic Pressure
Brake lines and brake 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 brakes 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 brake hoses typically results in:
- Brake fluid leaks
- Uneven pressure to wheels, causing the car to pull to one side when braking
5. Disc Brakes: Creates Friction By Squeezing
A disc brake has a caliper, brake pads, and brake rotor.
When the brake pedal is depressed, pressure through the brake fluid engages the caliper pistons, causing the brake pads to squeeze the spinning rotor. Friction between the brake pads and rotor stops the wheel.
6. Drum Brakes: Creates Friction By Pushing
When you engage the brake pedal, brake fluid pressure actuates the wheel cylinder, which pushes a pair of brake shoes apart and onto the insides of the spinning brake drum. Friction between the brake shoes and drum halts the tires.
You now know the basic chain of reaction from the brake pedal to the disc (or drum) brakes.
Let’s focus on the braking mechanisms, starting with disk brakes.
Understanding Disc Brakes
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. Disc brakes are preferably mounted on front wheels because they can handle more heat and have a faster braking response compared to drum brakes.
Here are the primary parts of a disk brake:
1. Brake Rotor (Brake Disc): 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.
Here are some issues associated with damaged rotors:
- Warped rotors or one with corrosion or brake pad deposit buildup can cause vibrations in the steering wheel and brake pedal when braking
- Heavy corrosion on rotor surface may cause loud grinding noises
- Cracks can develop in a rotor from temperature and repeated stress
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 are typically one of two designs — a floating caliper (pistons on one side) or a fixed caliper (pistons on both sides).
Faulty brake calipers can manifest these situations:
- A stuck caliper piston causes the car to pull to one side as a brake pad is still applied on one wheel
- A broken caliper seal leaks brake fluid, resulting in reduced braking power
3. Brake Pads: Stops The Rotor
Brake pads are mounted on the brake calipers, with their friction material facing the rotor. They come in different materials that 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 ¼ inch thick before you get new brake pads.
And here’s some of what happens with worn brake pads:
- A metal indicator creates a squealing noise when 75% of the brake pad is gone
- Excessively worn pads can cut into the rotor, resulting in a harsh grinding sound
- Unevenly worn pads cause the car to veer to one side
Next, let’s take a closer look at drum brakes.
Understanding Drum Brakes
Drum brakes are an older brake type with an enclosed design.
They’re more complex than disc brakes but cheaper to replace, and it’s also easier to install parking brakes in them. So, you’ll still find them on economy models or as rear brakes where less braking force is needed.
Because they’re a closed configuration, they overheat faster than disc brakes and have more tendency to experience brake fade.
Here’re the main pieces of drum brakes:
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.
Here are some issues that occur with brake drums:
- It’s subject to water ingress, and the water has nowhere to go until enough heat evaporates it. The water gets between the drum and brake shoes, adversely affecting brake performance.
- Drum expansion from excess heat creates a wider gap between the brake shoes and the drum’s inner surface. This causes a “long pedal,” where you’ll have to press farther down to get braking performance.
- Excessive drum wear may cause wheel cylinder pistons to slip out of their bore.
2. Wheel Cylinder: Pushes The Brake Shoes Onto Brake Drum
The wheel cylinder is located 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.
Here are some issues related to a faulty wheel cylinder:
- Worn pistons or rubber seals can leak brake fluid
- Pistons can get stuck from corrosion
3. Brake Shoes: Stops The Brake Drum
Brake shoes are curved metal pieces with a friction lining on one side. They’re mounted inside the brake drum, with the friction material facing outwards, towards the brake drum’s inner surface. Like brake pads, brake shoes come in a variety of material options too.
When you have worn brake shoes, this can happen:
- Grinding noises turn up when the friction lining wears down
- Rattling sounds can be pieces of peeled off, broken brake lining rolling around in the drum
- The parking brake is less effective if it uses worn brake shoes to hold the car stationary
We’ve gone through primary brake components.
Next are some indicators that you need a brake inspection.
5 Signs You May Need A Brake Job
If you’ve been following carefully, you’ll notice that bad brake symptoms can be similar for different braking system issues.
Here’s a lineup of the 5 usual suspects, and sometimes they come together:
1. Odd Sounds
A high pitch squealing often means worn brake pads that demand replacing. This is one of the more common issues.
On the other hand, grinding, rattling noises may indicate anything from damaged brake pads dragging painfully against a rotor, 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 one that sinks to the floor can mean anything from a brake fluid leak, air bubbles in the brake line, to worn pads.
However, 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 unevenly worn brake pads.
However, drifting might not even be a brake problem. It could be caused by unevenly inflated tires (possibly a punctured tire) or poor wheel alignment.
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 ABS brakes — 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, 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 certainly worth much more than a brake repair or new brakes.
Now, let’s move on to some FAQs on brakes.
4 FAQs On Brakes
Here are the answers to more brake topics:
1. 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 is more than the traction limit of the tires, 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 (ie. brake fluid) in your braking system. It’s essential to keep air out of a hydraulic system as liquid isn’t compressible, but air is.
- Brake Bleeding is a brake service that removes air bubbles from the brake lines. It’s usually done whenever any changes are made to brake components.
- Brake Pedal Feel describes the overall feeling of how brake pedal travel is perceived to affect braking output performance. For example, do you need to only tap the brakes a bit to stop?
- Brake Drag indicates how much the brake pad drags against the brake 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 of it is 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.
2. What Is The Parking Brake?
The parking brake system is a completely separate device that bypasses the hydraulic brakes. It typically employs the rear brakes and uses only cables and levers to work.
The parking brake keeps your car stationary, so it doesn’t move or roll off a slope. It’s also called an emergency brake because it can stop the tires if hydraulic brakes fail — just never do this at speed.
3. What Are ABS Brakes?
The Anti-Lock Braking System (ABS) is an add-on to the regular braking system. It’s designed to prevent wheels from locking during heavy braking, to avoid vehicle skidding or hydroplaning. ABS allows for safer, faster, controlled stops.
4. How Much Does It Usually Cost To Replace Brakes?
Replacing “brakes” typically refers to replacing your brake pads or shoes. The cost for new brakes varies based on vehicle make and model, location, and friction material used.
However, it can be between $150-300 per axle on average. Just keep in mind that a brake repair can involve more than just replacing brake parts.
Good driving practices include gauging sufficient braking distance, avoiding tailgating (to prevent emergency brakes), 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.
And if you ever need a simple solution to brake repair, you can always count on RepairSmith!
RepairSmith is a mobile vehicle repair and maintenance service, available seven days a week. Contact us for help, and our ASE-certified mechanics will drop by and get your car’s brakes fixed ASAP.