1998 Chevy Siverado 1500 2wd with a 4.3 liter engine. The brake pedal has pressure when the truck is off but with it running the pedal goes to the floor pretty easily. I have replaced the master cylinder, the brake booster check valve, adjusted the rear drums(discs in front), and bled the truck several times. I just can't seem to fix this problem and I don't have a vacuum gauge but I don't hear any vacuum leaks anywhere. Any ideas?
The brake fluid is also frothy in the master cylinder reservoir.
The brake fluid is also frothy in the master cylinder reservoir.