Been trying to sort my neglected brakes in time for this weeks MOT but made a blatent error the other week when I removed my rear calipers to get them serviced, and didn't clamp the brake lines. Obviously all the brake fluid bled out but didn't think much of it as I was going to bleed the whole system anyway. When it came to refitting the calipers and pressure bleeding the brakes everything seemed to have worked nicely. No bubbles, perfect pedal feel, jobs a goodun... until I switched the ignition on. Then the pedal goes completely to the floor. No brakes except a tiny bit of pressure right at bottom. Also start hearing a wooshing noise coming from the pedals when I press the brakes. Thought I might somehow have flipped the seals on the master cylinder but when I switch the car off again, the pedal feel comes back to perfect after a couple of presses. Again, switch it on again, nothing but carpet and wooshing. Read somewhere that it be the ABS pump that needs purging, which might explain why it all goes pear shaped when I switch the car on. Either that or I've destroyed the master cylinder? Any ideas?