Hydrovac

[eurostyle]

to eliminate a lot of guess work, you can check for engine vacuum at a non-ported vacuum source (e.g. pcv valve hose at the valve end) at idle speed and step on the brake pedal with the engine still at idle speed. if the vacuum level dropped with the brake pedal depressed, the control valve on the brake booster may be leaking atmospheric pressure into the vacuum chamber (front of the diaphragm) and causing a considerable leak. or check the system voltage with the engine running if the battery voltage drops with the brake lights on

thanks sir, iccheck ko po.