I'm new here and I need help. I'll try to keep this short. Trucks has 187,xxx miles and V6 engine. Replaced rear brake shoes, wheel cylinders, front brakes and calipers. Bled brake system per Haynes manual, R/R first then L/R, R/F and L/F last. With engine off brakes good, with engine running brake pedal goes all the way to the floor. Bled brakes again, no help. Then changed master cylinder, yes I bench bled master cylinder before I installed it. Pressed on brake pedal before I hooked up lines to it and it was very frim. Bled brake system one more time after I installed master and hooked lines to it. The brake pedal still goes to the floor. I have bled the brake system at lest 10 or more times, once even with the engine running. I don't know what els could be wrong. Hopfully you guys can help me out before I have to pay some one.

 

Do you hear a hissing sound when you press the brakes? - Possible booster failure.

 

Yes I hear a hissing sound. But I thought that if the booster went bad you would get a hard pedal with the engine running.

 

bad seal between the booster and master cylinder could cause it. if you're absolutely sure the brakes are bled (including the master cylinder)

 

Any up dates?