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Discussion Starter · #1 ·
installed a new m/c on 69 corvette. Replaced all 4 Caliper (professionally rebuilt ) also new rotors. Reason for the repair ,brake pedal was going to the floor .Bench bled m/c installed, and pressure bled entire system .Pedal hard, start car pedal travel to far down but not to the floor. Stop engine .re-bled. Pedal now goes to the floor every foot pump and will not return to hard pedal .After several trouble shooting try's found front left caliper to have air in it.If you pump very slowly m/c will begin to firm up.But once you crack open bleeder valve an close it ,pedal goes back to the floor an will not pump back-up at normal rate of foot pump .Old caliper on the left side did the same thing.After several, several times repeating these procedure(pressure bleeding and foot pumping ) I get the same results .Checked all hoses and fitting an found no leaks or swelling of hoses .Yet there seams to be a very small amount of air in left caliper.Not enough to result in no pedal after opening and closing bleeder valve to remove any air.Any chance the proportional valve could have something to do with the pedal travel.Have stepped on brake pedal very hard trying to make sure the valve was centered.Still no change.

:WTF
 

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I'm assuming you have manual brakes?

Simply, I think you still have air in the system, or possibly, a bleeder or line fitting is allowing air to be sucked in.

When you replaced the master did you perform a gravity bleed? That will usually eliminate air from the lines, which drain when the master and calipers are removed.

Did you have any problems bleeding the master? I have seen air get sucked in at the fittings at the master before. They didn't leak, but they sucked in air, which drove me bonkers for weeks trying to figure out the same thing you're dealing with.

Next, all four calipers are new, and they hold a LOT of air. As a rule I usually pre-fill the calipers before I even install them. Another tip, tap on them with a wooden handle or something similar which will help dislodge any air bubbles inside the master that are clinging to the caliper walls.
 

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Also be sure and bleed both inside and outside of the C3 calipers. I use a piece of clear plastic hose on the caliper air bleed when peddle bleeding keep the hose pointed up from the bleeder with fluid in at least an inch or 2 from the bleeder to keep from sucking air back into the caliper.
 

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Discussion Starter · #4 ·
Thanks to all that replied .After racking my brain for days . I decide to go back to my first intuition that the M/C was bad. I know the M/C I replaced was new but it seemed that it wasn't developing enough pressure because the pedal would go all the way to the floor even after bleeding. Made up two pressure gauges that I installed on the M/C in place of the brake lines . Found that the pressure would go to 160 psi only for a second and than drop to 80 psi with the pedal being held down. M/C pressure for dual reservoir should be above 630 psi each port. Auto supply replaced M/C with another one . I installed, an wouldn't you know it I have pedal and good BRAKES !! Here's a good web page that explains M/C.:smack

http://www.hotrodheaven.com/tech/brakes/brakes1_index.htm
 
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