Corsa B Brake Pedal Lost When Engine Started

[matthew1992]

hiya, i have a 1999 1.0 Corsa B for my first car, for its MOT we had to replace the rear brakes, since then we have had nothing but trouble. We have since replaced the master cylinder, servo, front discs and pads, front flex hoses, rear drums and shoes, rear cylinders and rear flex hoses. We have bled the system using a pressure bleeding kit and there is no air in the system at all. We now have a perfect brake pedal when the engine is turned off, as soon as the engine is started the pedal goes straight to the floor and loses all of its pressure. Any ideas on what it could be? Everybody i know has given up with it and doesnt know whats wrong. Thanks

[PRICER]

sounds as tho its some problem with the brake servo

[matthew1992]

thats what we thought which is why we changed it, didnt make any difference though