We Buy All Cars, Running or Not!

How a Car’s Brake System Works – What You Need To Know!

How a Car’s Brake System Works

The brakes are the most important part of your car. They can save your life or the lives of others. They can also stop your car from rolling down a hill when you are parked and if they are working properly, they will let you glide to a perfect stop. 

⚠️ If It's Broken, Don't Fix It - Get Paid Cash for Your Vehicle ⚠️


If something goes wrong with your brakes, you should get them fixed right away. If your brakes go out completely, you must replace them before driving again or you should get a new car.

Most vehicles these days have brakes on all four wheels and are operated by a hydraulic system. 

If you need new brakes it is helpful to know how they work and a bit about each component of a brake system.

What are Hydraulic Brakes

A hydraulic brake system is a braking mechanism arrangement which uses fluid that contains glycol ethers or diethylene glycol, to transfer pressure from the brake pedal to the braking apparatus. 

There are two different types of brakes; drum and disk. A drum brake. A drum brake is a compact round drum that contains a set of shoes. The drum brake rotates with the wheel. When you depress the brake pedal, the shoes are forced against the sides of the drum and the wheel slows down. A disc brake is comprised of a disc-shaped metal rotor that spins inside of a wheel.

A car’s front brakes are technically more important than the rear brakes when it comes to stopping a car.  When you hit the brakes it throws the car’s weight forward onto the front wheels. It is for this reason that disc brakes have become more popular than drum brakes. Disk brakes work better in the front. Drum brakes are stronger in the rear.

All-disc braking systems tend to be used on more expensive cars and high-performance cars. All-drum systems are generally used on older and smaller cars.

Master and slave cylinders

The master cylinder sends hydraulic pressure to the slave cylinder when the brake pedal is depressed. When you step down on the brake pedal, it depresses a piston that is located in the master cylinder that pushes fluid along the pipe.


The fluid is transmitted to slave cylinders which are located in each wheel. The cylinders are filled with the fluid and that forces the pistons out to activate the brakes.

Fluid pressure circulates evenly around the system. The piston in the master cylinder is not as strong as the combined surface ‘pushing' area of all the slave pistons. As a result of this, the master piston must travel several inches to push the slave pistons the short distance it takes to activate the brakes.

As a result of the set up, a strong force can be exerted by the brakes, in a similar manner to a lever with a long handle. It can carry a weighty apparatus a short distance.

Cars today are suited with dual hydraulic circuits. They have two master cylinders that work in tandem, in case one fails.

In some cases, one circuit operates the front brakes and one operates the rear brakes. In other cases, each circuit operates both of the front brakes and one of the rear brakes. There are other cars still in which one circuit works all four brakes and the other simply operates the front brakes.

When a driver uses the brakes a lot or rides the brakes, so much weight may be taken off the rear wheels that they will lock. This may result in skidding which is very dangerous. This is why it helps to have rear brakes that are made less powerful than the front.

The vast majority of vehicles have a load-sensitive pressure-limiting valve.  The valve shuts when heavy braking increases hydraulic pressure to a degree that might cause the rear brakes to lock, it will prevent fluid from flowing into them.

Top-quality cars often have intrinsic anti-lock brake systems that are equipped with sensors that can determine when the car is decelerating and if the wheels will lock.

The brakes in systems such as these are applied in rapid succession to stop them from locking.

Power-assisted brakes

Some vehicles have power assistance to lessen the energy needed to apply the brakes.

They get their power from the pressure difference between the partial vacuum in the inlet manifold and the outside air. They also have a servo unit that supplies the assistance which has a pipe connection to the inlet manifold.

There is a direct-acting servo between the brake pedal and the master cylinder. This pedal may operate the master cylinder directly in the event that the servo fails or if the engine is not running.

A direct-acting servo sits between the brake pedal and the master cylinder. The brake pedal pushes a rod which presses against the master-cylinder piston.

Brake pedals also work on a set of air valves.  There is a large rubber diaphragm attached to the master-cylinder piston.

When the brakes are not engaged, both sides of the diaphragm are exposed to the vacuum in the manifold.

When you depress the brakes, it closes the valve that connects the rear side of the diaphragm to the manifold and opens a valve that admits air from outside.

The higher pressure of the outside air drives the diaphragm forward and pushes on the master-cylinder piston. This assists you in breaking.

If the pedal is not depressed the air valve admits no more air from out of doors, so the pressure on the brakes remains the same.

When you let up on the brake pedal, the space behind the diaphragm is opened to the manifold again, so the pressure lessens and the diaphragm falls back into place.

If the vacuum fails as a result of the engine stopping, the brakes will still operate as there is a mechanical link between the pedal and the master cylinder. However, there must be a greater force on the brake pedal to apply them.

How Servos Work

When you apply the brake of a car it lets air in behind the diaphragm this forces the diaphragm against the cylinder.

There are cars that have an indirect-acting servo that is stationed in the hydraulic lines. It sits between the master cylinder and the brakes. This type of apparatus can be mounted in the engine compartment. You can mount it anywhere in the engine it is not necessary to put it directly in front of the pedal.

The servo relies on the manifold vacuum to issue a boost. Pushing down on the brake pedal causes hydraulic pressure from the master cylinder to build up. A valve will open triggering the vacuum servo.

More Details on Disc Brakes

A basic type of disc brake has a single pair of pistons. There may be more than one pair. There may even be a single-piston which controls both pads in the fashion of a scissor. It goes through different types of calipers – a swinging or a sliding caliper.


The actual disc in a disc brake turns with the wheel. The disc is mounted by a caliper, in which there sit small hydraulic pistons operated by pressure from the master cylinder.

The pistons push up against friction pads that hold onto the disc from each side, this slows or stops the disk. The pads are designed to cover a broad sector of the disc. In dual-circuit brakes, there may be more than one set of pistons.

The pistons move just a very short way to apply the brakes, and the pads just clear the disc by less than an inch when the brakes are released. There is no return spring.

When you depress the brakes, fluid pressure forces the pads onto the disc. When the brakes are not on, the pads barely clear the disc.


Rubber sealing rings around the pistons enable the pistons to slip forward slowly as the pads wear down. This way that little gap remains even and the brakes do not need to be adjusted.

Vehicles nowadays have wear sensors leads built into the pads. When the pads need to be replaced, the leads are exposed. This causes them to be short-circuited by the metal disc. A warning light will illuminate on the instrument panel.


More Details About Drum Brakes

Some drum brakes with a lead shoe and back shoe have just one hydraulic cylinder. brakes with two leading shoes have a cylinder on each of the shoes, they are fitted to the front wheels on an all-drum system.


A hollow drum inside a drum brake turns with the wheel. It has an opened back that is covered by a stationary backplate. The backplate has two curved shoes that carry friction linings.

The shoes are pushed outwards by hydraulic pressure moving pistons that are in the brake's wheel cylinders. This presses the linings against the inside of the drum to slow or stop a vehicle.

When the brakes on the shoes are forced against the drums by their piston. The shoes have a pivot at one end and a piston at the other. The leading shoe has the piston at the leading edge of the direction in which the drum turns. When the drum rotates it tends to pull the leading shoe firmly against it when it makes contact. This actually makes braking better and safer.


There are drums that have dual leading shoes. In such brakes, each leading shoe has its own hydraulic cylinder. Other drums have one leading and one trailing shoe. The pivot in these brakes is at the front.

This structure forces the two shoes apart from each other by a single-cylinder with a piston in each end.

This is not as effective as a  two-leading-shoe system. It is usually restricted to rear brakes.

In either type of drum brake, the return springs pull the shoes back a small distance when the brakes are released. The distance the shoe travels is kept short by an adjuster. Drum brakes may fail if they are applied too quickly. They heat up and won’t work correctly until they cool down again. Discs have better construction, are will not fade as often.

Many things can go wrong with your brakes and it is important to maintain them properly. Your owners manual should tell you how often to replace your brake pads, but generally, it should be about every 50,000 miles.  They should also be cleaned and lubricated on a regular basis.

If you have to get your brakes fixed the average cost should be around  $300 to $350. Replacing brakes can cost it cost around $500 to get new brakes. 

If you need new brakes you can get them replaced at an auto body shop or at the dealership. The dealership will charge you a lot more than an auto body shop, but they are likely to be quite well versed in working on the make and model of your car. 

An auto body shop will charge you less money and you will get to speak directly to the mechanic. Find out how long the autobody shop has been in business and what kind of certification your mechanic has. AAA maintains a list of qualified mechanics all over the country.

Selling Your Car

Car brakes should last a long time and of yours go out, it may be time for a new car. If you do need a new vehicle you can make money on the old clunker.


You can use the car as a trade-in when you buy your new vehicle, but the dealership is unlikely to give you what it is worth. You can sell your car online, but that can take months and it can be dangerous. Many criminals find their victims on online sites.


Sell Your Car to Us 

Cash Cars Buyers will give you a good price for your car. All you have to do is fill out our form and we will call you right back with an offer. 


Our form requests your name, email address, and phone number. We need to know the make, model, VIN number, and mileage of your car.


If you accept our offer, we will make an appointment to get your car. We will pay you in cash and tow it away for free.

© 2022 Cash Cars Buyer. All Rights Reserved. Terms & Conditions | Privacy Policy | Sitemap