I just pat a new master cylinder on my 68 delmont and I'am getting a real high pich whistle from the booster if I hit the brake it goes away momentarly and if I unplug the vacum it goes away. HELP thanks Sully

 

Was there a gasket on the cylinder base that you forgot? It sounds like a vacumm leak for sure, and is is probably a small hole or crack of some sort which is causing the whistle.

 

yes I put the new gasket on.

 

Maybe you could localize where at the MC the leak is somehow, not sure but there must be a way......hmmmm. If you know where it is, maybe then you could determine what is causing it and how to fix it.
does the power booster have an angled attachment on it made of plastic, maybe that is cracked or damaged.

 

Its not the booster,the booster is only a few years old and with the old master I didnt have a problem. I'am going away for the weekend so I will end up thinking about it over the weekend and mess with it when I get back. it has to be the seal between the master and the booster? I'll let you know if I figure it out. thanks Sully