your new mc should have a new rubber with it. DONT drive the car without the rubber, it holds the brakerod in the mc. if you were to push the pedal, and the pedal came back and the rod fell out of the mc, no brakes
Do I have the wrong master cylinder? I got a disc brake master for the year and model of my car. When I stick the rod in the new master cylinder with the old rubber still on the rod it does not stay.