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Old 03-09-2009, 12:08 PM
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lost pedal pressure... Help!

I have a 1979 Nova with the factory disc/drum setup. I have not modified the factory brake system, stock MC and booster. One day while power braking the car I noticed that when I came to a stop that I had lost pedal pressure and the car feels like it has a slight vacuum leak. I can pump the brakes build pedal pressure to stop the car, but it will not hold any pressure. I checked the fluid level and was full. I have searched the forum and knowledge base. Any suggestions will be appreciated!

Leemoses

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  #2 (permalink)  
Old 03-09-2009, 12:13 PM
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If you were power braking the car I would suspect a wheel cylinder over heated and lost its seal. They don't need to be leaking much to give you a bad pedal.
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Old 03-09-2009, 01:00 PM
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Just loading the rear suspension, no smokey burnouts... Keep the suggestions coming!
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Old 03-09-2009, 02:56 PM
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It sounds like you might have a crack in the diaphragm in the power brake booster. After all, it is probably 30 years old. Just a thought. Good luck, TR
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Old 03-09-2009, 07:18 PM
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I suggest you keep looking for a vacuum leak. Do you have a vacuum canister or are you pulling vacuum directly on the booster?
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Old 03-09-2009, 07:21 PM
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Why would a vacuum leak cause a soft pedal?
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Old 03-09-2009, 09:44 PM
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Vac leak would cause a hard pedal.... it's a leak somewhere no doubt
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Old 03-10-2009, 05:20 AM
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Quote:
Originally Posted by leemoses
I have a 1979 Nova with the factory disc/drum setup. I have not modified the factory brake system, stock MC and booster. One day while power braking the car I noticed that when I came to a stop that I had lost pedal pressure and the car feels like it has a slight vacuum leak. I can pump the brakes build pedal pressure to stop the car, but it will not hold any pressure. I checked the fluid level and was full. I have searched the forum and knowledge base. Any suggestions will be appreciated!

Leemoses
When you say "lost pedal pressure", are you saying that the pedal was soft and went to the floor?
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Old 03-10-2009, 06:36 AM
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yes, the pedal at first goes to the floor, after several pumps it will build pressure to stop the car
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Old 03-10-2009, 06:44 AM
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no vacuum canister, vacuum is routed directly from the intake to the booster
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Old 03-10-2009, 06:44 AM
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I have a 77 nova and the pedal would go to the floor slowly and not have any pressure but if I pumped them the car would stop fine until the pressure I pumped up bled off. The cause of that problem and maybe yours also, as ive seen more of this problem then any other is your master cylinder. There are O rings in the shaft of your master that get worn out and allow pressure to bleed past with out having a leak. So if you don't see any wetness around wheel cylinders I would replace the master they are only about $25.00 and im sure it is way over due anyways.
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Old 03-10-2009, 06:46 AM
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You need to check for brake fluid around your calipers and wheel cylinders and behind the master cylinder. You are leaking somewhere. or your M.C. is bypassing.
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Old 03-10-2009, 08:28 AM
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Quote:
Originally Posted by leemoses
I have a 1979 Nova with the factory disc/drum setup. I have not modified the factory brake system, stock MC and booster. One day while power braking the car I noticed that when I came to a stop that I had lost pedal pressure and the car feels like it has a slight vacuum leak. I can pump the brakes build pedal pressure to stop the car, but it will not hold any pressure. I checked the fluid level and was full. I have searched the forum and knowledge base. Any suggestions will be appreciated!

Leemoses
This is a classic symptom of a failed master cylinder. If the internal seals of the MC go bad, the pedal will slowly fall but you will not lose fluid. A new MC for this car is cheap (unless you care about a correctly date-coded one).
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Old 03-10-2009, 08:48 AM
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Soft brake peddal

You say your peddal is soft utill pumped up right?
If your booster was the problem your peddal would be harder to push than non assisted brakes.
So most likely you have a leak of some sort.(internal or external)
If no fluid can be found leaking at the wheel cylinders or between the master and the booster then I'd change the Master Cylinder it is likely bypassing internally (leaking by the seals in the master cylinder between front and the rear )
Test it ;Pump up your peddal and hold some pressure and your peddle slowly sinks the your fairly sure it is the master leaking internally.
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Old 03-12-2009, 11:24 AM
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Gentleman
I come bearing news...
First, all who blamed the MC as the culprit you were... correct. Second, all who blamed air in the lines you are also... correct. We have a case of a faulty bleeder screw and a clapped out MC. The clogged banjo bolt prevented the air from being bled from brake lines, after the MC was replaced.

Thank you all for your recommendations!
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