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Discussion Starter #1
ok my car build is actually a 63b 1967 custom 500 2 door sedan, (galaxy frame or platform) I believe they made less than 10k of these, but I have a 545 (460) 871 blown fitech dual throttle body injection motor, it makes 16.5 to 17 inches of vacuum at the check valve on the booster, the booster is a 7 inch dual diaphragm (space is limited) a 1 inch bore corvette style dual equal bowl master cylinder, the lines are std 3/16 new rubber lines the front calipers are the metric s10 calipers and disc conversion kit from scarbird, the rear axle is a 8.8 cobra with factory calipers and vented rotors with a 4:56 trac loc, now I can apply vacuum with a pump to the booster and it test fine pedal drops about a inch but when I start and drive the car the pedal is EXTREAMLY HARD and real compression on the brakes and the car will not stop very well,, I did order a 9 inch booster that's fairly thin it may fir and I ordered a corvette style 15/16 bore master cylinder I am really at a loss of what is mis matched obviously something its all new except the rear calipers and I just had there apart and made sure they wasn't froze or any kind of binding so it goes good takes of great cruses nice but wont stop lol .... any ideas I did call cpp and mpb and they all said the booster and master cyl is fine the problem may be because of the metric calipers not being able to take the volume of fluid and that in my case I may need to go to a smaller bore master because the bigger the bore the less pressure the more assist I need or smaller bore the greater the pressure the less assist I need and or less pedal ratio ,,,,,, as I gaze into the stars.... ...... h e a d l I g h t s ooooooooooo lol not big into brakes so any ideas please let me know and I will report back on the booster and master cylinder,.,.,.,
 

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Test the booster by pumping the pedal with engine off to evacuate vacuum , pedal will go hard . Still holding foot on pedal , start engine and pedal should drop . If not booster not operating as it should .
 

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Are you using a external vacuum pump to the booster or engine vacuum?

A big cam and the lower vacuum plays hell on power brakes, especially when coming out of throttle.

Might try a vacuum reservoir canister if you haven't already. If you end up needing a external pump you can use the reservoir with it.
 

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Discussion Starter #5
the cam profile is set up for the fuel injection as fitech requires to deliver between 12 and 18 hg and the actual inches of vacuum is 17hg at the throttle body and at the booster check valve and that valve checks good and was replaced anyway

there is no vacuum pump

and no reservoir
 

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If it was in my shop I would have ran it on the rolling road brake tester to see exactly what brakes were operating correctly and what the pressure readings were at each wheel and took it from there dependant on results .
 

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You mentioned above, the brake pedal is fine at idle but once you drive its hard. That sounds like a vacuum issue. Are you coming straight off of the intake for vacuum or the throttle body?

Remember the old black juice cans that you would see on the older Fords that were used for a vacuum reservoir? You have anything like that laying around to try? I think a reservoir 'might' help. Just a thought.
 

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Discussion Starter #8
okay well the pedal has about a 1/2 inch of travel once you press it once or twice weather the car is running or not at idle or under throttle and when you do drive it the brakes barley slow it down and after you shut it off I can pull the check vale out of the booster and it has loads of vacuum tomorrow I am going to measure my pedal length from pivot to rod pin and see if I am in fact at 4 to 1 ratio swing, its really driving me nuts I have brake pressure at every wheel they release when take you foot off it really feels like you took your new car or newer model car remove the booster vac line plug it off and drive it that's the type of hard pedal I have, and I have been giving the reservoir idea some thought and the only concern I have is there is no power assist anywhere in the pedal travel, I would agree if there were some kind off assit but there is nothing so im not sure that would help but then again I dunno ill try anything at this point lol I have a car with 22k in it and I cant stop
 
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