The published numbers for pedal ratios are wrong…..
Using the method above, I come up closer to 7 to 1.
Thanks KD. I posted those numbers
as they are what most engineers
would agree are optimal for the
different configurations. Many
variations can occur when deviating
from factory systems and/or
An example would be the system I
I've read some articles where they
recommend moving the booster/MC
to obtain the 4:1'ratio, and drilling
a new hole in the pedal arm.
The bellcrank changes the
ratio of the pedal arm as the
bellcrank pivots. The ratios
are taken from the attachment
of the bell crank as the pedal arm's
Consider me lucky ?
I mounted the dual diaphragm
booster in the designated location
for a manual MC in a 1940 Plymouth
pickup. Then mounted the brake
pedal assembly (cut down to fit
under the dash) from a 1985 Dodge
Diplomat. The booster rod lined up
perfectly with the booster, and the
rod was the correct length. I used
the bellcrank from the Diplomats'
Went with a four disc system. (Ford
Granada front, Jeep TJ rear).
After install, there was a minute
amount of pedal travel before
brake pad contact, so I installed
2# residual check valves in each line.
(keeps the pads from backing off the
rotors), and placed an adjustable
proportioning valve for the rear
circuit. The brakes work flawlessly.
MC is a 1-1/8 bore, the booster is
a rebuilt CORDONE unit from a 1985
Chrysler LeBaron. Brake lines are
steel 1/8" I'd. (note pic 2).