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Discussion Starter #1
Hello everyone. Just got through replacing the brake system on my 68 GT that has front disk brakes. everything new from the master cylinder to new shoes and calibers. The distribution block and proportioning valve have been rebuilt and double checked that they were done correctly. My problem is that I cannot get the pedal to stay firm when they are bled. The brakes will pump up and have a good firm pedal and when you take your foot off and leave it off a few seconds the pedal will go to the floor. I have bench bleed the MC sever times and I am getting fluid to all four wheels. Bleeding from RR, LR,RF, LF, the traditional way of having someone pump the brake while I bleed.I even back bled using a syringe.

Anyone have any idea why the pedal won't stay firm?
Any help/suggestions on what to try would be appreciated.
 

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New brake calipers installed with the bleeders pointed up?
 

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Sounds like you did everything right...hmmm, the pedal drops to the floor huh? I assume it power brakes - so what happens if the car is running? Does it studder or act funny when you apply the brakes? I'm wondering if your Booster is Busted? It doesn't make sense that the pedal would drop to the floor though...? The fluid has to be going somewhere....can you pump the pressure back up and it stays firm if you continue to hold it? I wonder if your MC is still having an issue and leaking into the booster?
 

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Discussion Starter #4
Motor is not in the car. They are power brakes and you can pump them back up and they will stay firm as long as you hold pressure on them. Yes woodsnake the bleeders are pointing up. No leaks into the booster.
 

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Have you adjusted the rear shoes so that they are just dragging the drums? Either that or the check valve in the master is not working properly.
 

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Hmmmp - I'd say it's gotta be the M/C bleeding by then - either the balance is not even between the prop valve or it's blowing through internally maybe from the from to the back reservoir. I think the front is the safety portion and maybe that's what actually holding all the pressure?...see if the front one actually accumulates more fluid after you play with it....
 

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Discussion Starter #8
First of all, thanks for the suggestions. I'll try to answer them all. Yes the rear brakes are adjusted to where they drag a little. The caliber bleeders are facing "UP". I Thought woodsnake way saying that they should be facing up. I'll change sides with the calibers today and let you know if this was what was wrong. Bad69cat, now that I think about it fluid comes rushing back into the back reservoir that controls the front brakes. If I have the calibers on the wrong side I can see how the trapped air would force the fluid back after releasing pressure and thus causing loss of pedal the next time you press down. I'll let everyone know, and thanks again for everyone's help.
 

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Caliper installation guide:

 

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Discussion Starter #10
Woodsnake, you are the man. I changed sides on the calibers so that the bleeders pointed back, and immediately got a full hard pedal that stays up,by just gravity bleeding them.

Thanks again for all the help.
 

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Glad to be of assistance. This has come up many times on the board...I was jus the first person to respond!
 
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