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Discussion Starter #1
I've been through the power brake servo system on my '78, making sure there are no leaks. It tested good when I did a leak-down test in the fall. Now, I find that if I start the car in the morning, I can drive off and the brakes are terrible until I get the revs up high for awhile, then they work fine for the rest of the drive no matter what speed the engine is at. Is it normal for the system to take awhile to get the vacuum established, or is this indicative of some kind of leak?
 

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No, not normal; should build vacuum pretty much instantly. I wonder if the check valve is messed up? It should allow suction in the direction of the manifold (pulling from the booster), but not the other way.

The air valve has to work too, so it's not just a matter of the chamber holding vacuum.

Andrew
 

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Discussion Starter #4
It was the check valve. Well, sort of. I pulled the hose off of the servo and there was no suction. I revved the engine and I heard a "POP" and suddenly, there was suction. I think a piece of rust or grime of some kind was intermittently blocking the hose fitting on the manifold. They work great now, but I'm wondering what got sucked into the intake.
 

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Pop may just have been the check valve seating. Same thing happened to mine I had to spray some lube in the valve and free it up.
 
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