If you get all the air out- - - - -and that can be a big IF, the brakes will work, but you're going to have a low, stiff pedal. Normally, the master cylinder connected to the pedal is simply a trigger device, something to control the Hydrovac. If it has to become the primary source of brake pressure, it must force the fluid through the inoperative booster unit, which takes up most of its capacity. Low pedal- - - -poor brake operation. I don't think I'd take very many test drives that way!
Jerry
