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C3 Brake Question

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Old 08-30-2011, 02:09 PM
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scrappy76
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Default C3 Brake Question

On my 76 I have been trying to get the brakes working correctly and here is my question ,

If I can press on the pedal easy I have a good stopping power and holding power, but if I press really hard, the pedal will start to stop the car but then go to the floor and barely stop. Even if I pump them up it still does the same thing. Do I still have air in the lines ? or is something else wrong like the master cylinder or the brake booster going bad ?
Old 08-30-2011, 03:40 PM
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LB66383
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A couple of questions...

Are you losing any fluid? Is either reservoir going down?

If you're sitting still and press and hold the pedal, does it stay firm, or does the pedal slowly sink to the floor?
Old 08-30-2011, 09:48 PM
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scrappy76
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Originally Posted by LB66383
A couple of questions...

Are you losing any fluid? Is either reservoir going down? Not losing any fluid.
If you're sitting still and press and hold the pedal, does it stay firm, or does the pedal slowly sink to the floor?
If I am sitting still like at a light I can have my foot on the brake and it hold fine, but if I press really hard , it will sink to the floor.
Old 08-30-2011, 10:09 PM
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noonie
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Rule of thumb.
If you can pump it up quickly and it holds a higher and higher pedal then you have air.
If it sinks while trying to hold a pedal, then you either have an external fluid leak or if none, then an internal master leak. Easy way to check for external leaks is to track the fluid level in the reservoir after many pumps or lots of use.
Old 08-31-2011, 06:03 AM
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scrappy76
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I have no fluid loss at all. If I slow down normal and come to a stop the pedal holds fine. while sitting at a light it holds fine, does not go to the floor at all. its when I am sitting there at a light and if I push real hard, the pedal will sink. If I have to hit the brakes hard and fast, the pedal will hold for a short then sink as I push harder.
Old 08-31-2011, 06:30 AM
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MrJlr
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I think it needs bleeding.

Old 08-31-2011, 08:22 AM
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bobbarry
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Originally Posted by scrappy76
I have no fluid loss at all. If I slow down normal and come to a stop the pedal holds fine. while sitting at a light it holds fine, does not go to the floor at all. its when I am sitting there at a light and if I push real hard, the pedal will sink. If I have to hit the brakes hard and fast, the pedal will hold for a short then sink as I push harder.
I'd bet donuts to dollars that it's the master-cylinder; what you describe sounds like a seal in the master that holds under moderate pressure, but fails under very high pressure.
Old 10-20-2011, 07:31 AM
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scrappy76
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I am still trying to figure out my problem. I do have some more info to add though. When I do step on the brake fast and hard I hear like air sound under the dash near the pedal and the cars idle sounds like a miss in it till I left off the brake. could there be something wrong with the brake booster? too much vacuum ?

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