One way to carry out a brake system operating check is to press the brake pedal for several times when the engine is off and observe whether there is any change in the pedal reserve distance. After that, push down on the pedal and start up the engine; this will be called normal operation if it goes slightly downwards. For an air tightness test, switch on your cars' engine and shut it down after approximately one or two minutes. Slowly depress the brake pedal a few times, if each depression leads to lesser travel of the pedal, then this means that the brake booster has an air-tightness. To further confirm air tightness, let's push our foot on brake and turn off the engine using a foot on a brake pedal. If there is no variation in pedal reserve travel even after holding it for 30 seconds, then you can be sure that your power brakes are properly sealed. Don't take apart any Power Brake Booster units since they require special tools together with professional skills from those who do so. When removing power brake booster apply specific procedures based on make and model of your vehicle because some models may require disconnection or removal of additional components such as cowl tray, air filter housing and brake lines. While installing a new Power Brake Booster ensure proper clearance of pushrod adjustment where necessary. After installation check and set Brake Pedal Height, Free Play and System Bleeding as required by standard.