okay i just changed the brakes on my 1997 honda civic dx coupe, the brakes are really hard like it's supposed to be when the car is turned off, but as soon as you turn the car on the brake pedal goes all the way to the floor when you step on it, it's really soft.. i've bled the WHOLE system already, theres no air but i don't know why the pedal is sinking to the floor when i start the car... any ideas?