Hi guys. The other night, I came home from driving my 69 and noticed the hiss of a bad vacuum leak. To make a long story short, The leak is at the bottom of my master cylinder toward the back where the flange bolts to the booster. The leak is not the flange but under the master cylinder where there seems to be a thru bolt hole that runs from side to side. I can plug the thru hole with my fingers and stop the leak and my engine runs smoothly. Otherwise it stumbles and runs very rich. What could be causing this? I can unplug the vacuum hose from the booster and plug it with my finger and that also stops the leak.
Any help would be appreciated.
Thanks, Jody.

On my 69 cutlass, there is a hole on the bottom of the master cylinder near the flange where it bolts to the booster. I allows brake fluid that may get past a defective master cylinder plunger to escape without being forced to leak into the power booster. Hence, I suspect that you have a vacuum leak in the inside of your booster and it is pulling air into it thru that "drain hole". Not sure of the internals of a booster so I can't help fix that, save buying a new booster.

Has anyone experienced this problem before?
Jody

Once, on a 69 Charger. Though rare, boosters do sometimes go bad. It sounds like you will be springing for a new one.

Hey Jody, contact Steve Gregori at this
place (http://www.brakeboosters.com), he has the right stuff and is fair on his prices.