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Vacuum Leak Hiss from brake pedal ?


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First off my car is a '75 280 with a 78 rear end and threaded steel brake lines.

I did a "brake" search and found that when most people apply the brake pedal and it hisses their rev's go UP-well mine tries to kill the engine completely if i keep it held down. My pedal goes right to the floor on the first pump but after 2 more i can get pressure but the brakes still suck!! I know i need shoes in the back. Also I'm slowly loosing fluid. We just replaced the right rear wheel cylinder and the brake master cylinder. Can you guys please tell me if this is my booster or a master vac ($267! from MSA). Thanks a million guys...

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Well the Z guy who put on the wheel cylinder and master cylinder bled the master cylinder while i pumped, so im sure he's seen it work if thats what you mean-im a noob on the whole brake booster/master vac issue, i just know something hissing like a vaccuum leak when i pump the brakes and it tries to kill my engine at idle.

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Sounds like a bad booster and master to me, basically you're leaning out the engine really bad when you step on the brakes, because it's sucking air through the brake booster diaphragm. You can pull the hose off of the booster and suck on it, and if it doesn't hold vacuum then you know it's bad.

 

The master should never lose fluid. Pull it off and look inside the booster. I bet you find that it's got a bunch of fluid inside. The only other option for loss of fluid is that you have a leaky fitting or a bad caliper or wheel cylinder.

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