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Discussion Starter · #1 ·
I have a '41 ford coupe with a home-fabricated brake pedal-to-booster setup. The master cyl to booster rod clearance is good, the problem is the pedal sits a bit too low during actual braking and there is no adjustment to correct this or anyway to modify the brake pedal/arm to fix the problem. There is an adjustable rod that sits between the booster and the brake pedal clevis, which when adjusted for about 3/16" preload on the booster internal spring causes the pedal to engage braking at the correct height. That setup seems to work well, with no dragging brakes or other noticeable problems. Can there be an issue over time with that setup?
Thanks,
Tom
 

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If the pedal is hitting its max height against some kind of stop on the pedal bracket and this rod is depressing the piston your riding the brakes to some degree.

If you modify this bracket removing this stop that will allow the petal to be raised without depressing that piston that would be just fine.

You could also look at ways to modify the pedal or bracket itself to suit your needs.
 

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I'm in the process of adjusting mine now. If you have 2" of travel before things start to happen it's just fine. Know the feeling about the pedal to close to the floor. If you have a pressure style brake light switch in your system have someone watch the lights as you depress the brakes. If you have several inches of travel all is good. Jack the car up and test spin the tire while pressing the brake will give you good piece of mind about drag.
 

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Discussion Starter · #4 ·
Thanks, I will do the check with the wheels up. I know the booster internal spring already has some preload (it doesn't rattle)...so the slight increase will probably not do any harm.
 

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Discussion Starter · #5 ·
OK, I took the booster apart to see how it worked...and the internal diaphragm spring is under a LOT of compression (the uncompressed length is about 12 inches and the compressed length is under 3 inches and it is a stiff coil spring... I'm using a 7" single diaphragm unit). But...the middle valve, the one that closes the opening between both sides of the diaphragm goes shut after only about 1/8 inch of input shaft travel. So, my idea that you can preload the spring is OK, unfortunately, the smallest amount of shaft movement will either cause a premature boost or full boost because of that valve closing. I guess the only options without a system geometry change are to make sure the gap between the master cylinder and booster shaft is as small as possible (like .040" as some say) and set the pedal-to-booster play very close to zero or no more than 1/16" less.
 
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