Formula
for Master Cylinder Pressure
I
have been asked hundreds of times how do you determine the pressures
output of the master cylinder. The following information will
help you determine the proper size master cylinder:
To figure how
much pressure your master cylinder is putting out:
C = pedal
ratio
D = pounds of pressure apply by your foot
E = area of you master
cylinder
F = pounds of pressure out of the master cylinder
C X D /(divided by) E = F
Example: If you have a 1" master cylinder the area equals
1/2" x 1/2" x 3.14 = 0.785 Square Inches. So, 100 pounds
(of applied foot pressure) X 6 (pedal ratio) divided by 0.785 = 764 pounds of
pressure.
If you have a 1-1/8" master cylinder, 100 psi
X 6 (pedal ratio) divided by 0.9935 = 604 pounds of
pressure.
Here is some info on master
cylinder with "constant" of 6 to 1 pedal ratio and 100 psi being applied.
3/4"
master cylinder = 1359 psi
13/16" master cylinder = 1158
psi
7/8" master cylinder = 998 psi
15/16" master
cylinder = 870 psi
1" master cylinder = 764 psi
1-1/8"
master cylinder = 603 psi
DO NOT Try to use a OEM master cylinder smaller than 1" without calculating
the volume requirement. It is like choosing between jump off a cliff
or a plane, how do you want to die? Remember you can not do
anything after you run out of brake fluid, but you can still press
on the brake pedal harder.
If you are upgrading you brake
system check the following about your master cylinder:
1. Does it have a built in residual valve? If
yes, replace it with a disc/disc or disc/drum master cylinder that
matches your calipers.
2. When replacing the master cylinder ALWAYS buy new.
Determine the size bore based on the caliper design and piston sizes
being used.
3. Master cylinder used with a booster will generally have
a dimple in the back of the bore. This dimple will mate to
the flush mounted rod on the booster.
4. On installation be sure to check for a small amount of free play
so the master cylinder is not preloaded.
See residual valves, power boosters
and brake pedals for additional information.
Copyright reserved by
Dean Oshiro. Reproduction without written approval is a violation
of Copyright Laws. 1994-2006
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