A hydroboost brake booster is a power brake assist component on certain types of vehicles.

To bring your vehicle to a stop, the braking system requires an immense amount of pressure, sometimes up to two thousand pounds per square inch of pressure. Generating such high pressure with the brake pedal and hydraulics alone without any power assistance can be extremely difficult. Therefore, years ago, vehicle manufacturers incorporated a device to lend power assist to the braking system to make it easier to press the brake pedal.

This device, called a power brake booster, is mounted between the brake pedal and the master cylinder (hydraulic pump) that exerts force on the brake fluid to activate the brakes. The brake booster multiplies the force exerted by your foot on the brake pedal.

There are different forms of power brake booster, depending on where they obtain the power assist. Most vehicles rely on engine vacuum from the intake manifold for this purpose. Some vehicles, however, such as those with diesel engines or turbocharged engines, do not produce enough vacuum to adequately power up the brake booster. A hydroboost brake booster relies, instead, on pressure from the power steering system. As pressurized power steering fluid runs through the hydroboost system, it drives an internal piston that creates the power necessary to assist the driver with braking.