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Offline ToniJ1960

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brakes still
« on: March 13, 2013, 04:22:42 PM »
 Still having the pedal drop on my 1978.Ps Pb car. The light would come on once or twice on my way home. Seemed like the master cylinder. I replaced it, still had the problem, found a drop on  the front line so both front lines and both front hoses were replaced. Still the pedal would drop under light foot pressure. So I thought maybe it was a bad mc the first time and I replaced it again. Still dropped so I had both wheel cylinders replaced they needed to be done anyway. But its still doing it.

 Now heres the best description I can give.

 The pedal drops so slow under light steady pressure it takes 30-40 seconds to drop, and once it gets to below the gas pedal level it drops faster. When the engine is off it doesnt drop far enough to activate the switch/light. When it is running it will eventually. It still never goes completely to the floor.

 After it drops so far, the next time I press the brake pedal I can hear air rushing in or out somewhere around the pedal area.

 Anybody feel like offering any advice suggestions experience?

Offline Pinto5.0

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Re: brakes still
« Reply #1 on: March 13, 2013, 05:15:35 PM »
Are you still losing fluid in the M/C? If so you still have a minor leak. If not you have trapped air somewhere. Do repair shops still pressure bleed? It may be worth the price to solve it.
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Offline ToniJ1960

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Re: brakes still
« Reply #2 on: March 13, 2013, 05:18:52 PM »
 It looks like the levels staying pretty much the same in the reservoirs. I dont see any on the ground on  the rotors etc. The lines and fittings are dry.

 I did read somewhere the booster can fail to seal off the brake lines but I never heard of that.

Offline Pinto5.0

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Re: brakes still
« Reply #3 on: March 13, 2013, 05:28:08 PM »
There's no fluid in the booster. The vacuum loss won't make the pedal drop, that's a fluid issue.  No drop in level pretty much means air trapped somewhere. Try bleeding each wheel 5 times starting with the RR then LR then RF then LF. Dont let the M/C drop below half & never let the pedal up(even a tad) while a bleeders cracked open.
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Offline ToniJ1960

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Re: brakes still
« Reply #4 on: March 13, 2013, 05:39:27 PM »
 The weird thing is when the engine is off the pedal wont drop far enough to make the light go on. It will when the engine is running though. ARgh mysterious brake issues I hate them.

Offline pintosopher

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Re: brakes still
« Reply #5 on: March 13, 2013, 06:26:55 PM »
Tonij, It sounds like your Brake booster is "helping " the Pedal drop while the engine is running, Because that's what a power brake booster is supposed to do. It's pushing the fluid down further into the air bubble that is still in the lines. Re bleed, and be sure that you lose no fluid into the Booster diaphragm, or there might be a seal issue there. Pressure bleeding is my solution to all soft pedal issues when all else is good.
 Good luck..
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Offline half pint

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Re: brakes still
« Reply #6 on: March 28, 2013, 11:23:44 PM »
another approach you could try is to gravity bleed the system.  when i've had stubborn brake systems, that's what i've done.  how you do it, is to remove the master cylinder cap, make sure the M/C is FULL of fluid.  start at the right rear wheel, the one furthest from the M/C...crack the bleeder screw and wait.  keep an eye on it and DEFINITELY pay attention to the M/C level.  it is critical to keep it filled.  once you see fluid coming out of the bleeder, close it off and move to the left rear.  fluid will most likely come out of it fairly fast.  then move to the front right...it might take a while, but when fluid finally starts coming out, close it off and move to the left front.  again, fluid will most likely come out relatively fast.  close that one off.  again, DO NOT let the M/C run low on fluid during this process.  once you're done, put the M/C cap back on and test your brakes out.  you should have absolutely NO air in the system. 

that's how i've always dealt with stubborn-to-bleed hydraulic systems...be it clutch/brake systems...good luck bud!