What Does a Brake Booster Do?

January 27, 2012

Over the years, the modern automotive braking system has enjoyed many innovations, including the widespread implementation of the brake booster. Designed to help improve braking performance and safety, the brake booster is an essential component of the braking system that helps allow accessibility to any driver regardless of strength or size, all thanks to its ability to manipulate engine vacuum.

Braking System Overview

While using them is generally quite simple, the modern automotive braking system itself is a complex and often times misunderstood system. By depressing the brake pedal, a shaft is pushed forward. This shaft is attached to the power brake booster which uses engine vacuum to help give the brake pedal some added force, which helps to counter the high pressures found in the braking system. Combined with the power of your foot pressing the brake pedal, this shaft helps push a piston inside your brake master cylinder, which in turn displaces brake fluid through your braking system. This fluid makes it way through the Brake cylinder, through the proportioning valve, and is divided up so that proper amounts reach each wheel, where they act on the Brake slave cylinders which actually clamp your pads against the brake rotors and slow your car.

Why Use a Brake Booster

In the old days, vehicles commonly used drum brakes, which naturally provide some of their own power assistance. Once disc brakes started to become more common however, the lack of braking assistance started to become quite noticeable. Brake systems work at rather high fluid pressures, and without the assistance of the brake booster, would result in a rather hard, and difficult to use brake pedal. While this in itself may not be bad for someone used to a manual braking system, or in very good physical shape, for many people it would simply be too hard to comfortably depress in the amounts required for every day driving. This would mean that proper stopping ability would be limited by personal strength, which erodes much of the accessibility that the modern automobile enjoys, and poses a safety concern to everyone on the road.

How a Brake Booster Works

As you depress the brake pedal, your pedal linkage causes a shaft to move forward in response to your foot, and as this shaft moves forward, it interacts with the brake booster and master cylinder. The brake booster contains a diaphragm that separates its interior into two parts, with both in a partial vacuum. As the brake pedal is depressed, it causes a valve inside the booster to open, which in turn allows air into one side of the booster. This difference in pressure on one side helps to push the piston inside the brake master cylinder forward in response to the brake pedal, which in turn slows and stops your vehicle.

A brake booster increases the force the brake pedal exerts on the brake master cylinder by using engine vacuum and pressure. Without a brake booster, even the simple act of slowing your car would require substantially higher amounts of effort and incur greater amounts of fatigue. The brake booster does not brake your vehicle for you, it simply offers a helping hand.

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