 Hi, I'm Bob Hulcomb from Apex Automotive and great bearing to Massachusetts. Today we're going to talk about your hydraulic brake booster. This device is bolted behind your hydraulic master cylinder. The master cylinder is connected to your brake pedal. When you apply your brake, it pushes a rod against the master cylinder. This rod is in between the master cylinder and your brake pedal. The rod runs through the brake booster. As the engine runs, vacuum is generated and pulls against a large diaphragm on the backside of your master cylinder. When you apply brake, the diaphragm or the vacuum from the engine also pulls forward. It allows you to put a little bit of energy on your brake pedal, but a whole bunch of energy goes to your brakes. That's why it's easy to stop your car with a vacuum assist hydraulic brake system. If you should have a leak in your system, you'll hear a distinct whistling noise, a vacuum leak. It sounds like a vacuum cleaner, but in reverse, you'll hear a hissing sound, and this could be your brake booster leaking. Typically, you'll hear it when you're driving the car. They do make a lot of noise and they hold a lot of vacuum. The brake booster is about this big, and it's a reservoir for vacuum. There's a one-way valve between the brake booster and your engine. As your engine turns, it pulls air out of the booster, and that one-way valve doesn't allow it to go back in. If you look at your booster and underneath the booster, between the vacuum assist booster and a hydraulic master cylinder, if you see fluid, that's a bad sign, and that'll need to be addressed right away. As that's a leak in your brake system, right at the booster. These are a couple of quick tips about how to tell if you have a bad brake booster. I'm Bob Holcomb from Apex Automotive and great bearings and Massachusetts.