Snoopysvet said:Issue -
The brake pedal goes to the floor but the car stops.
If I plug the vacuum hose to the booster the pedal is firm and does not go to the floor, I can drive the car around the block with no issue other than the pedal being very firm.
I successfully swapped the Master Cylinder about 8 months ago with no issue and I am familiar with odd sequence of bleeding the brakes in C3s.
I assume the booster is bad however I thought if it was not working the pedal would be very stiff
If the master cylinder was bad would the pedal go to the floor if the vacuum hose to the booster was disconnected?
yes reading links and sub links may be a P.I.T.A. but it leads to ANSWERS
your question basically contains two separate but interacting systems, the vacuum booster which allows you to apply minimal brake pressure but have it amplified at the master cylinder significantly, and the master cylinder which actually applies hydraulic pressure to the fluid.
look thru these links, AND DIAGRAMS CAREFULLY
if the booster is not working the petal in most cases will be down near the floor but not on it, , as the movement in the booster assembly is already taken up,the brakes will still work but probably require a great deal of effort to be applied as in both feet and putting all your weight on the petal.
the info you posted earlier makes me think the booster is leaking or its connection to the brake master cylinder is loose but the master cylinder is functional