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Power Brake System Basics

Brake booster

The power brake system in your car or truck is something you take for granted each and every day. The fact that you can step on the brake pedal and apply gradual, even pressure until your car slows to a halt — or stomp on it hard so that you stop as quickly as possible — is the result of decades of innovation and engineering. Along the way, different types of braking systems have been developed, tested and sold to customers around the world.

Let’s take a quick look at how and why power brakes work on a modern car.

Boosting Brake Pressure

Brake warning sign - power brake system basicsA power brake system wasn’t always a given on mainstream automobiles. As recently as the 1960s and 1970s it was possible to buy cars that had “unassisted” brakes. The job of generating enough pressure to send fluid to each drum so it could clamp down and slow a vehicle was entirely given over to the driver’s foot. When disc brakes hit the scene, it was necessary to add some type of power assist, because they didn’t offer the same pedal amplification that drum designs did — plus, it just made sense for automakers to add power brakes so that they could up-sell customers on a brand new safety feature.

Vacuum Assist

There are different types of power brake system designs out there. For many years, the most common was the vacuum assist, which uses the vacuum generated by a gasoline engine’s operation to move a diaphragm inside a vacuum booster. By opening a valve on one side of the booster when the brake pedal is pushed, on-rushing air pushes the diaphragm against the vacuum, which in turn moves a piston in your braking system’s master cylinder, sending fluid to each wheel’s brake caliper. Take your foot off of the brake, and the valve closes so that the vacuum can push back against the diaphragm and release the fluid pressure.

Other Power Brake System Designs

It’s also possible to use a hydro-boost braking system that employs the same pump that powers a vehicle’s power steering system to send fluid to the brakes. These are often used in diesel trucks, which don’t benefit from an engine vacuum like gas models, but some conventional automobiles also offer this design. Popular on trailers are electric braking systems, which rely on a system of magnets that, once activated by an electrical impulse, operate a drum brake system to slow down each wheel. Electric brakes are useful because they eliminate the need to install a full hydraulic braking system — a trailer can simply draw power from the vehicle that is towing it to run its brakes.

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

Photo courtesy of Wikipedia Commons.

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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