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Old 09-27-2010, 04:02 PM
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proportioning valve

can any one tell me what are the symptoms of a bad proportioning valve.

i am having a problem were my front brakes are not holding. the car wont hold after hitting 1500 rpm. also when in Park i pump up the brakes then give it gas the peddle will lose power. i changed the master and i changed the booster. everything in the car is basically new. the car has been setting. i also have the SS braided lines for my brakes but they all bleed good. please any help.
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Old 09-28-2010, 08:06 AM
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With the engine off, press the brake pedal several times to bleed off any residual vacuum pressure.

Hold the brake pedal down and start the engine.

If the pedal drops slightly, the booster is good.

If the engine has been modified, that can cause the brakes to not receive enough vacuum pressure. If you don't have one, a reserve tank may help.

With all four wheels off the ground and the engine running, have someone turn your front wheel while you very slowly press on the brake. When the wheel grabs, hold the pedal and have them move to the rear wheel. If it still turns, slowly press more pedal until the rear grabs. This would indicate the fronts are coming on before the rears. The reverse and I believe the correct condition condition would be for the rears to come on "just before" the fronts.

Here is a drawing of correct plumbing and a great site for tech info.

http://www.mpbrakes.com/uploads/docu...lumbingpdf.pdf
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Old 09-28-2010, 09:14 AM
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Quote:
Originally Posted by mac350
my front brakes are not holding. the car wont hold after hitting 1500 rpm. also when in Park i pump up the brakes then give it gas the peddle will lose power.
I would check the check valve and its grommet for the booster. If it's leaking or not holding vacuum, a loss of manifold vacuum will immediately translate into a loss of booster assist.

It is usually located where the vacuum hose enters the booster housing. The one shown below is for a GM- it ALWAYS helps to give the make, model, year, etc. of your vehicle, BTW.

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Old 09-28-2010, 04:30 PM
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Do you hear any air leaking anywhere ? What are you working on anyway ?


Cole
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Old 09-28-2010, 05:21 PM
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Maybe the brake pads arent aggressive enough
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