I have a MPBrakes power brake set up that includes an electric vacuum pump, 9 inch booster, and a dual bowl MC with 1 1/8 inch bore. My pedal is harder than hell and my brakes are actually worse than before the installation of the booster. I checked an I am pulling 21 inches of vacuum with the vac. pump. The shop that did the install says that the problem is that I have 4 wheel disks with 4 piston calipers each and that the MC is not properly sized for the disks. MPBrakes says that the size of the MC is fine. Could it be that the booster is itself bad? If so, how do you test for a bad booster?