1965 runs rough first 2-3 times applying brakes

[Timotbird]

Is it considered normal or abnormal for the engine to run rough while applying the brake for the first 2-3 times at start up and in park. I swing the “swing away” steering wheel over to the right to right as a precaution after starting. The idle evens out after the booster has created enough vacuum and is no longer drawing from the manifold. It takes a couple brake applications to normalize the idle.
I had the booster out a year ago and it seemly held vacuum when tested.
Just wondering

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[64ZCODE]

Would seem you have a vacuum leak in the booster or in the vacuum line that connects from the intake manifold to the booster. Check the vacuum line for leaks, including where it connects to the intake and to the booster. But also have the booster checked out. If it's old and has never been replaced, the diaphragm may be leaking. Plus, fluid from the master cylinder can leak into the booster which will degrade the diaphragm over time.

 

[Timotbird]

Would seem you have a vacuum leak in the booster or in the vacuum line that connects from the intake manifold to the booster. Check the vacuum line for leaks, including where it connects to the intake and to the booster. But also have the booster checked out. If it's old and has never been replaced, the diaphragm may be leaking. Plus, fluid from the master cylinder can leak into the booster which will degrade the diaphragm over time.

The master cylinder was replaced when the booster was out last year, so no leaks there. It is the original booster so a potential problem.
Because it held vacuum when out of the car, I put it back in. When I last checked, you needed to send in your booster core before they would send a replacement I have checked and replaced the vacuum hoses to the booster. It also has a new check valve.
But thank you for confirming a vacuum leak during the first couple pumps of the brake after start up is not considered normal and needs further investigation.

 

[64ZCODE]

Sure! I just replaced the booster and master cylinder on my '64. We could have had the booster rebuilt at a place here in the San Francisco bay area, but decided to go with a new unit from ABS Power Brake, and they wanted the old booster in exchange. During the install, my mechanic told me that the old vacuum line to the booster should be replaced so that full vacuum gets to the booster. We did that, installed the new booster and master, and now the car stops like it never stopped before.

One thing to add to my original comment is that you should check for vacuum leaks elsewhere in the system too. If it's leaking anywhere, that will affect how much vacuum the booster sees and how long it takes to reach full power.

 

[Timotbird]

Well, it appears to be the booster. If it wasn't leaking vacuum previously, it is now. I briefly pinched off the vacuum hose to the booster, applied the brakes and no change in idle. As soon as I removed the pliers and reopened the vacuum hose, the idle jump up and ran rough when applying the brake. So leaky booster.
I'll check out ABS Power Brake. Thanks again for your responses.