Silverado Brake Problem - Low Pedal
I have a 00 Silverado Z71. The brake pedal currently is going all the way to the floor when the truck is running. If I shut the truck off the brake pedal can be pumped and the brake pedal will raise back to the normal height. I have not done anything recently with the brakes. The brake fluid is about 1/4" below the max line. I do know I was just about to change the rear pads and rotors. What would explain this sudden loss of the brake pedal? Why only when the truck is running? My plans are to change the rear pads and rotors and see if this makes a difference. If not, I am planning on bleeding the lines. Any other ideas? How do you know if the Master Cylinder or Power Brake Booster is bad?