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3 Methods for Testing Power Brake Booster Failure If the vacuum is leaking, damaged, or the internal components within the power brake booster are damaged, it will not work correctly. The vacuum powers an internal bladder, which supplies the force to the hydraulic brake lines. This is why power brakes only work while the engine is started. It works by drawing power from a vacuum that is created by the engine during operation. The power brake booster also helps to provide the force needed for the right amount of pressure to create an efficient application of force. The brake booster helps to supply the correct hydraulic pressure in order for the brake calipers to apply pressure to the brake rotor and create friction established by the application of the brake pads to the rotor. Each of these actions must work together in tandem to stop the vehicle. To safely stop your vehicle, three scientific principles need to occur - leverage, hydraulic pressure, and friction. In order to understand how the power brake booster fits into the modern braking system, it’s critical to explain how brakes work. In the next few paragraphs, we’ll explain how this critical component works within the brake system, and a few pointers to help you diagnose and determine if the power brake booster is the root source of your problem. If the brake booster fails, it can lead to a soft brake pedal or even complete brake system failure. The power brake booster is used to supply brake fluid throughout the brake lines, which permits the system to work effectively. We all understand that the brake system is essential for the safe operation of any vehicle, but what is not commonly known is that a leading culprit of brake system failure in older cars, trucks, and SUV’s is the power brake booster. However, when you press that brake pedal and you notice the car is not slowing, that tends to grab your attention rather quickly. Under normal operation, most car owners never consider the inner workings of the brake system.