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?

 

i had the same problem with my truck but had a reck because of it you might want to call chevy about that because its a big problem with those trucks but nobody has pushed the issue with chevy about that . i guess it would probily get them in alot of trouble.

 

Here is the lame reason that I had the same problem. There is an STB on the parking brake which states that the parking brake pushes the pad against the rotor 24/7, running or not adding that the result is a weak brake pedal. They wanted $300 to fix until I called GM's complaint line and was directed to another local dealership who replaced the unit and my problems went away. There was also another STB with concerns reflecting an issue with 99-02 1500s ABS system. The dealership that I went to for the parking brake issue replaced something related to the ABS system as well. I have had no problems since 2002 after getting GM to stand up and fix an extremly dangerous issue. I urge you to look for your STBs as many will be addressed by GM even out of warranty.
GL
Greek

 

well, If your brake booster is bad you would get a very hard brake pedal, a bad booster wont cause the pedal to go to the floor!