Brake problems with the '76 New Yorker

I was wondering if any of you knew anything about the brake system on this car. The brakes lose pressure when you press and hold the pedal. It bottoms out, and the brake light comes on. This happens, yet the car leaks no brake fluid and the master cylinder appears to work normally. I was thinking the problem is the brake booster unit. Also, when I press the brake pedal with the engine off, I hear air escaping. I don't know if this is normal or not, but I thought I'd mention it. I would think that any brakes work on the same principles, but then again, I've never had to work on this type of thing. Any ideas?

Thanks,
Jon
:ylsuper

Sounds more like a bad master cyclinder than anything else.

secondary seal in the master cyclinder is bad

I definately agree with them but just so u know if it was the booster it would be a harder pedal, cos the boosters function is to boost/assist in pressure applied to the brakes, thus making the pedal softer.
Just a bit of handy info.