I have a quick question for you guys. I think that the brake booster in my '80 Z28 is bad. When I brake, the pedal will slowly go to the floor. We thought it was from a lack of vacuum at first so we put a vacuum canister on it, but I still have the same problem. I was wondering if there is any way to somehow check the booster to see if it is the problem or if I need to look elsewhere. Any other ideas are welcome too. Thanks.

 

change the master clinder.

 

I with camSS on this. Do this. Start the car up. Let it idle and now stop the car. Do it now or do it in the morning so you can feel the difference.
With the car off, keep pressing the brake pedal until it gets hard. OK, that took the air out of the booster. Restart the car and let the booster fill back up. Come morning you can do the same thing is pump the brake pedal till you bleed the air out = Did the booster need to be replaced if it holds air overnight like normal.

I am back to 73cam's suggestion if she holds air.