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Discussion Starter #1
First, I want to apologize if there is an answer to my question in this thread I searched and couldn’t find one.

Here goes:
66 GTO, 400 with mild cam and .030” over, tri-power, and M21

Idle is reading about 850 to 900 rpm

Problem:
Brake pedal goes to floor at low idle and if I bring the idle to about 1,000 problem solved, but I don’t believe that is the real solution.

Do you have suggestions?

Thanks for the anticipated help!
 

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There should be a check valve on the booster. It fits into a rubber O-ring/seal, and your vacuum hose to the engine attaches to it. I am assuming you vacuum hose is attached at the back of the carb or a fitting on the manifold to provide full engine manifold vacuum.

The check valve can go bad as can the rubber seal. That is where I would start.

Then if that does not do it, it is possible the rubber diaphragm inside the booster has gone bad in some way and is leaking vacuum.

That is where I would start.
 

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Discussion Starter #3
There should be a check valve on the booster. It fits into a rubber O-ring/seal, and your vacuum hose to the engine attaches to it. I am assuming you vacuum hose is attached at the back of the carb or a fitting on the manifold to provide full engine manifold vacuum.

The check valve can go bad as can the rubber seal. That is where I would start.

Then if that does not do it, it is possible the rubber diaphragm inside the booster has gone bad in some way and is leaking vacuum.

That is where I would start.
Jim,
Thank you very much for the help it is greatly appreciated!!
 

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Problem:
Brake pedal goes to floor at low idle and if I bring the idle to about 1,000 problem solved, but I don’t believe that is the real solution.
Does the car stop? pedal goes to the floor??? how can that be unless there is no brakes? :eek:
 
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