Brake issues

My Duster has disc front and drum rear brakes it has been driven 7000 miles and worked
fine all of a sudden the brake peddle goes to the floor when you sit and hold the brakes on in gear I have adjusted the rear brakes and they are snug there are no leaks anywhere I can find and if you pump the brakes when the car is not running along at 50 or so it seems to hold pressure however when you are running it seems to work until you slow down and are idling in gear. I have replaced the vacuum hose to the booster didn't seem to make any difference. The vac booster was rebuilt 3 years ago. Does that sound like a problem with the master cylinder or with the vacuum booster.

I don't get what you are saying. First, the vacuum booster is never going to be the cause of a pedal to the floor.

Are you saying you GET a pedal and it sags slowly to the floor? If so, master is leaking internally, IE cups cylinder walls are worn

Master cylinder bypassing. Need to replace it.

SGBARRACUDA said:

Master cylinder bypassing. Need to replace it.

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SGBARRACUDA said:

Master cylinder bypassing. Need to replace it.

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Thats what I was wondering I thought it might be the master but before I did anything I wanted to make sure. Since the vac booster had been replaced and didn't want to rule it out however. Is it worth rebuilding the master or should I just replace it and start over?

If your wanting to rebuild it to maintain originality than yes. Other wise I would just replace it. I would imagine a kit will cost more than a complete cylinder.

SGBARRACUDA said:

If your wanting to rebuild it to maintain originality than yes. Other wise I would just replace it. I would imagine a kit will cost more than a complete cylinder.

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No I am not trying to maintain numbers on it it has some 73 parts and its a 70 so I think I will just replace it to keep it simple and easy.Thank you for the help I appreciate it.