Anyone ever use one of these to diagnose a problem? Several years ago I upgraded the car from manual (drums on all 4) to power brakes (front disk, back drum) and it feels like I'm stopping the car with the back brakes. The back tires lock up easily and during a somewhat hard stop the car nose dives (after the backs lock up), I'm guessing that the front brakes are coming on late and weak. I've bench bled the master cylinder twice and bled the entire system atleast 4 times, I see no air bubbles coming out. The vacuum gauge reads 8 to 8.5 (250/260 @ 050 cam) and the combination valve is too close to the headers (I'm going to relocate the combo valve).

I called Master Power and they said the correct way to diagnose the problem is to buy the pressure gauge (it's only &50.00) but I'm a little confused as to how one would keep air from getting into the system when attaching the gauge at the combination valve. If I have someone hold the brake pedal down while I disconnect the line and install the gauge wouldn't there be air in the fitting that the gauge is attached to? And wouldn't that air give me a false reading? Also, do you start the engine so the brakes have power assist when obtaining a reading?

Sounds like you didn't install the disk/drum proportioning valve when you did your brake upgrade.

Sounds like you didn't install the disk/drum proportioning valve when you did your brake upgrade.

The kit comes with a combination valve, I'm assuming that a proportioning valve is part of that combination valve.