Brake Booster Parts, Types, and Functions

With technological sophistication, doing certain things has become increasingly seamless in almost all spheres, including automobiles. Car manufacturers constantly include features that make a car more practical. One such technological advancement in cars is the introduction of a brake booster that makes stopping a car effortless.

Generally, a brake booster is a safety braking system component that uses a vacuum to increase the force applied by a driver on a brake pedal—invariably increasing braking power and letting drivers stop with minimal effort. The brake booster comprises several parts working together to achieve this. So in this article, we will discuss the brake booster parts, but first, let’s see the types of brake boosters.

brake booster diagram

Types of brake booster

The black diaphragm device is standard equipment found in the engine firewall, usually by the driver’s side with the brake master connected to it.

There are basically three types of brake boosters, each differentiated based on what they use in generating the force used to stop the car. They include.

Vacuum brake booster

This is the most commonly used brake booster out there, and chances are your car is currently using one. Vacuum brake boosters are probably common because of their simple design. It typically uses the engine vacuum in normal fuel engines to increase the force applied on the brake pedal. Here, a vacuum diaphragm attached to a vacuum port on a car’s intake manifold increases the brake force.

A vacuum brake booster may be utilized with the standard power brakes or nonintegral anti-locking brakes system. Brake boosters are standard equipment in almost all cars. So should something go wrong with them, you would need to apply more force yourself to stop the car, which is quite stressful.

Therefore, your best bet will be to fix or change. Technically how much you spend depends on the brake booster and which part is faulty. For example, vacuum brake booster parts may cost around $200, whereas other types of brake booster parts may go as high as $500 or more.

Vacuum pump booster (Electro hydro brake booster)

This brake booster is commonly found in hybrid and electric vehicles not capable of producing enough vacuum for a traditional power booster. An electro-hydro booster utilizes high pressured gas accumulator and a vacuum pump to increase the force to stop the car.

Generally, a vacuum pump brake booster can be driven mechanically or via electric motors. While this type of brake booster is common among electric and hybrid vehicles, it can also be used in diesel engines. A vacuum pump brake booster also comes in handy in high-altitude regions where naturally aspirated engines can’t produce sufficient vacuum for the brake booster.

Hydraulic brake booster hydro booster

Hydraulic brake booster utilizes hydraulic pressure created by the power steering pump instead of the vacuum pressure to multiply the braking power to stop your car effortlessly.

This type of brake booster is often found in diesel vehicles when the engine doesn’t allow for the size of a vacuum brake booster. And can be used on vehicles with or without an anti-locking brakes system (ABS).

Brake booster parts

The brake booster consists of several components that work collectively to multiply the braking power used to stop your car effortlessly. But here are the major brake booster parts.

brake booster parts list

Shafts or booster shafts

Shafts are the small round component on the booster and are used to link the brake pedal and master cylinders. There are basically two types of shafts in a brake booster— the primary and secondary shafts.

The primary shaft is connected to the brake pedal at the driver’s side and used to transfer braking force to the diaphragm to boost the pedal force. This shaft typically opens and closes the atmospheric valve, so fresh air can enter and leave the brake booster to push the diaphragm.

The secondary shaft mechanically connects the brake booster, and brake cylinder used to transfer increased pedal force from the power booster to the brake master cylinder.


Valves regulate the air and the vacuum used by the brake booster to stop your car. A brake booster uses two types of valves, namely, atmospheric and vacuum valves.

The atmospheric valve is situated at the driver flank of the brake booster and helps in controlling the amount of air entering and leaving depending on the brake pedal movement. The way this valve operates is simple; it opens to release air and closes afterward.

The vacuum valve, otherwise called a one-way valve, is placed at the master cylinder flank of the brake booster. And is used to trap the vacuum inside the brake booster. A one-way valve allows only one action—either air entry or exit. So in the case of a brake booster, the valve only permits air to leave and not enter inside the brake booster vacuum side.


A brake booster spring is used to regulate the primary shaft and diaphragm. The springs are of two types—primary and secondary, with the secondary spring larger than the primary.

The primary spring is located at the driver’s side of the brake booster and helps return the primary shaft to its original position after the pedal is released. It also helps in regulating the opening and closing of the atmospheric valve.

The secondary spring is placed at the master cylinder side of the brake booster and helps return the diaphragm to its original position after the brake pedal is released.


The diaphragm is placed between the vacuum and air side of the brake booster, providing an airtight separation between both compartments. It helps push the master cylinder with assistance from the secondary shaft.


The body is the outer covering of the booster that houses all other components. It serves as a shield against foreign objects that can destroy its components and protects the system from failing in the event of a clash.


Q: Can you rebuild a brake booster?

Whether or not a brake booster can be rebuilt depends on the type of booster and its condition. If the entire component is not too damaged, you can rebuild it using some old parts. All you need is a brake booster repair kit which may contain valves, a diaphragm, rubber part, and some other components.

The cost of this kit will also depend on your vehicle model; a Ford brake booster rebuild kit may cost more than a Toyota. If, however, the brake booster is badly damaged, dented, rusted, or broken, you may not be able to rebuild from the old one. In this case, you have to get all the parts needed to make a new brake booster.

Getting and fixing up these parts, too, depends on the brake booster type. For instance, because of its simplicity in design, a vacuum brake booster parts might be easy to get and put together. In contrast, it may be a tedious process getting vacuum pump brake booster parts or putting them together. Hence, many often go for a replacement instead of building.

Q: What is attached to a brake booster?

The brake pedal and master are attached to a brake booster. The brake booster is divided into two chambers by a flexible diaphragm. While your brake pedal is attached to one side of the brake booster, the master cylinder is attached to the other side.

Q: Is it expensive to fix a brake booster?

Whether it’s expensive to fix a brake booster or not, it depends on the type of brake booster and the severity of the damage. If only a few parts need to be replaced, it will be cheaper. If it is severely damaged, you will need to rebuild it or get a replacement.

Depending on the type of brake booster and vehicle model, a power brake booster replacement can be anywhere between $300 and $1200. Generally, brake booster parts cost can be as low as $100 or as high as $500 or more. For example, truck brake booster parts may cost higher than parts for small vehicles.

Labor, on the other hand, lurks around $100-$250. To get repair shops near you, simply type brake booster repair near me on your browser and pick an option. If, however, you are doing the replacement yourself, you could save as high as $250.

Q: Where are the parts number in a brake booster?

The parts number is the same as the item number, usually between 6-8 digits depending on the brand. It is written on the sticker placed on either the pack used to package the booster or on the round part of the booster.  The sticker depending on the brand, also carries other information like place of production, name of the producer, a scan code, and other numbers.

Q: What supplies vacuum to the brake booster

Where the vacuum comes from depends on the type of brake booster. In gasoline engines, the engine supplies vacuum to the booster. Here, a vacuum hose connected to the intake manifold can pull out air from the engine, creating a small vacuum.

In other automobiles, like electric and hybrid cars, a vacuum pump is used to supply a vacuum for the brake booster. In contrast, cars with diesel engines use hydraulic pressure from the power steering to create a vacuum. The vacuum is the power or force applied to the brake pedal to boost its stopping power.

How much vacuum is produced by the booster depends on the size of the engine vacuum and diaphragm. Usually, the larger the diaphragm and vacuum reservoir/side, the greater the power released to stop the car. This means larger vehicles will require a bigger vacuum booster and vice versa.


Brake booster parts work collectively to provide enough stopping power to stop your car effortlessly. To rephrase it, the brake booster won’t function properly if any of its part go bad. If the booster is still new, changing only faulty parts could save you a lot; otherwise, rebuild or go for total replacement. When replacing parts, use only parts that match your brake booster and car’s capacity.

For example, vh44 brake booster parts will not function like vh40 brake booster parts. Consequently, any mistake you make as regards using the right part or booster will invariably affect the power exerted from the brake booster. Which could result in you putting more or less pressure to stop the car.


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