Pull the plug on the rear bottom of the hydrovacs cannister. If brake fluid comes out your hydrovacs shot. These are designed to only hold an ounce or two of fluid.
To see whether your hydrovac holds vaccum, hook a vaccum gauge up to that hole and start the engine. After about 30 seconds turn the engine off and check the gauge. You should read at 17-20 pounds. It should also take awhile for the reading to go down.
If it doesnt, chances are the control valve diaphragm is shot or the check valve is clogged. If the diaphragm is shot, you need to rebuild the hydrovac. The check valve is located in line from the lid of the cannister to the intake manifold. It should have 4 screws holding it together. Pull it apart, after being used for however many years its usually safe to say that some gunk or fluid will stick that valve one way or the other.
It works by being pulled upward by enegine vaccum. When the engine dies, gravity takes effect letting it drop and sealing vaccum pressure inside the cannister so you get one more good power puch of the brakes. Anyways, clean it up real good and make sure theres no scratches on the little brass valve. If there is you may be able to polish it up or you may need a new check valve. Unless the valve is stuck up, it wont effect the hydrovac when the engines running.
Check this out for a rundown of how they workAnother test, push down the pedal slightly with the engine off. Turn on the engine. If the hydrovac is working youll feel the pedal move slightly downward as the vaccum engages the booster.
Jeff
