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What Is a Brake Booster And Why Do You Need One?

Master cylinder, including a brake booster

Asking “what is a brake booster” takes you to the heart of how modern braking technology works under your vehicle’s hood. Once upon a time, drivers had to rely on very basic mechanical braking setups that channeled the foot’s force on a pedal to each corner’s stopper. Luckily, today’s cars have a much more reliable, controllable and safe way to distribute braking force.

Let’s take a look at how this technology works, and discuss its role in your car or truck’s braking system.

Heavy Foot

Master cylinder

Manual braking systems relied on mechanical leverage to send hydraulic fluid through the system with enough force to push the pistons or the drum cylinders at the front and rear wheels. They did this by translating the travel of the brake pedal into the much shorter action of the master cylinder’s piston into the even smaller distance traveled by each individual brake caliper or drum component. This force reduction is like using a long lever to amplify your foot’s strength on the pedal.

Use the Force

Today, brakes use power assistance to ensure fluid is forced to the pistons (or in rare cases, the drum brake cylinders) as quickly as possible and with as much force as necessary. So, what is a brake booster? It’s the component that’s responsible for providing that extra helping hand.

The most common type of brake booster is a vacuum booster, which takes the vacuum generated by gasoline and uses it to create a partial vacuum inside the booster. As you push the brake pedal, a shaft moves through the booster on its way to pushing the piston in the master cylinder. It also opens a valve inside the booster, allowing air to enter one side of it (which is separated into two halves by a diaphragm). The pressure differential between the two sides adds extra force to the master cylinder piston.

It’s a simple, yet very effective system for increasing braking force without giving your right leg too much of a workout. There’s a valve inside the brake booster that preserves the vacuum even if the engine shuts off, so that you don’t lose braking assistance if your vehicle stalls. It’s also important to note that since diesel engines don’t generate a vacuum of their own, they require a separate vacuum pump to operate the booster. Electric vacuum pumps are also occasionally used on gasoline vehicles to ensure constant, steady vacuum for the brakes.

A Boost of Hydropower

Not all systems use engine vacuum, however. On many diesel-powered trucks or vehicles that tow heavy loads, a hydroboost system is used instead. Hydroboost makes use of the hydraulic pressure offered by the vehicle’s power-steering pump to generate even more stopping power than can be provided by vacuum alone. You’ll sometimes see a hydroboost system used on supercharged and turbocharged vehicles, as well.

Whether vacuum-, electric- or water-powered, brake boosters have made driving easier and safer for all vehicles on the road.

Check out all the brake parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on brake boosters, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

Benjamin Hunting View All

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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