What affect does master cylinder bore/piston diameter have on braking performance? I expected the brakes on my deuce to perform better than they do. '47 Ford front brakes, '65 Mustang rear drum brakes, and a master cylinder out of a '74 Ford Courier. I don't know any specifications of this master cylinder nor do I know how that affects the brakes. All of my tri-five Chevy's stopped better (all with stock brakes) than my deuce. This truck is 1880 pounds and the Chevy's are 3,000+ pounds. Any advice? Thanks.
Larger m/c bore = less pedal travel & more effort Smaller m/c bore = more pedal travel & less effort If I'm not mistaken your rear brakes are Duo Servo and your fronts are not. Meaning your front brakes have very little benefit from servo effect whereas your rears ARE benefitting from servo effect, but in an ideal world - it'd actually be better the other way around. STILL at 1,800 pounds I'd think it wouldn't be all that terrible. Any way you can hook up a pressure guage and see where you're at??
Bigger piston, harder pedal, shorter throw. Smaller piston softer pedal, longer throw. If the system is bled correctly and has the right adjustment, it really should work ok with either setup. Damn, you guys type fast!
My guess is that the Courier M/C is too small a bore for the brakes you are running. The M/c bore has everything to do with mechanical advantage, (leverage if you will). I have always matched my m/c bore size to match the brakes. Power vs. manual will often change bore size also. I can't remember if 47 Ford brakes are "self energising" or not, this will effect pedal effort as well. Is the pedal too hard or too soft? Does your pedal move a lot, close to floor, or is it near impossible to push?
Early Ford brakes used a 1 1/16" Master Cylinder, if you can duplicate that, your brakes will have a better feel and stop better. Most of us use the 1" Master Cylinder as a replacement and you get longer pedal travel and not quite as much pressure. HemiDeuce.
First off, thanks for the replies. The pedal moves quite a and but I have to "stand on it" to get to stop quickly. I don't know the pedal ratio, but it is stock Courier. My guess is the master cylinder doesn't move enough brake fluid for the wheel cylinders to work properly.
We are gettting off track here. Smaller mc bore produces more braking force but requires mre pedal travel. The ratio of master bore to wheel cylinder bore diameter is the key. A bigger master bore wll give you worse brakes not better as far as force goes. If you apply 500 pounds force to a pston with an area (square inches) of .5 or 1/2 square inch to a wheel cylinder of 1 square inc area you will get double the force on the the brakes at that wheel cylinder than if you had a master with a piston with an area of 1 square inch. But you will have to push the pedal twice as far to displace the same volume of fluid. Formula for area of a circle is 78.54% of the diameter X diameter (bore X bore X .7854) (because an circle contains 78.54% of the area of a square of equal dimensions. ) Put the wheel cylinder area on top and the MC piston area underneath . Divide and you will have the advantage or disadvantage ratio. The calculation is very similar to gear ratio work where the formula is Driven over Driving Don If you thought the formula was "Pi R squared" please remember, "Pies are round" Actually this formula avoids any confusion with the circumfernce formula (2piR vrs piR2) so it works well and does not have never ending decimals either because it doesnt use Pi which is one of those never ending numbers.
I think you are going to find eventually that the problem is in the way the front shoes are contacting or not contacting the drums. Those brakes are not self energising so the linings have to be arced(machined) to fit the diameter of the drum perfectly. Take the shoes and drums to a full-service brake shop, preferably one that does lots of big trucks and have the shoes arced to fit the drums. If the drums haven't been turned recently have them done too or you will not have good brakes. Fords of various years had either fixed anchor bolts or adjustable anchor bolts. If they are fixed anchor all you can do is put them together and cross your fingers. Adjustable anchors have a cam-action excentric bolt and lock nut with the bolt protruding past the nut so you can put a wrench on it. These are very tricky to adjust so you should consult a manual for the procedure.
When Power Brakes first came out (and maybe even today), manual brakes had a smaller bore sized Master Cylinder than the same car with Power Brakes...the booster curing the "hard pedal" situation. The aluminum Master Cylinder I'm using on my 32 has a 7/8" bore...manual disc brakes on all four corners. I'm HOPEing it will work...
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