Originally Posted by Diseasel300

WRONG!!!!!!!

The vacuum assist is to help PUSH the pedal down, not pull it back up.

Without the vacuum assist, it is hard to get sufficient brake pressure to diagnose a master cylinder unless it is extremely worn. When the vacuum builds to operate the booster, it's MUCH easier to push the pedal down. Since you have more force available to push the pedal, smaller leaks and faults will show up.

A sinking pedal is a sign of a leak or a failing master cylinder. If you find no leaks anywhere (check caliper seals, hoses, ABS pump, etc) suspect the master cylinder.

Originally Posted by Diesel911

Try it, it is a common test.
Although what I have read is you press the pedal down a 1/4-1/2 inch with the minimum pressure on the pedan and when you start the Engine and vaccuum gets to the Power Brake Booster the Pedal pushes back up.

The reason it does that is because when you forst start and Vacuum gets to the Booster the internal valves try to center the innards of the Booster.

Originally Posted by Diseasel300

I can see that with 1/4-1/2" pedal travel if you have a dual-diaphragm booster, but only in that case.

With a single-diaphragm or any more than the absolute bare minimum of pedal travel, pulling the pedal back up is detrimental, not beneficial to the operation of the booster's entire purpose.

Think about what was suggested above - if the booster has enough power to overcome you flooring the pedal without boost, what chance do you ever have of applying the brakes? It would be working against you, not for you.