Elite Veteran
Posts: 689
  
Location: Winston Salem, N.C. | on a 56 plymouth, I am adding power brakes by using an 8" new dual diaphragm master cylinder power brake unit for 1955-60 cheys. It is a common street rod booster unit, a universal model. Result is weak pedal. With normal braking, it is OK, but if I press pedal hard, as in an emergency, pedal goes all the way to the floor and I have no brakes. Two thoughts have been suggested to me.
1. Plymouth supplied a 2 arm swing out tool, back in the day, to seat properly the brake shoes to the wheel cylinders. We don't have that. Someone else said, you don't need that, they said my problem is:
2. the modern master cylinder that street rodders use is built to be used with disc brakes, not drum brakes.
thank you for any advice based on your actual experience.
Jerry Whitfield
Winston Salem, NC |
Expert
Posts: 3775
 
Location: NorCal | I agree on the pedal ratio, manual brake FL's typically had a pedal ratio of 6:1 or 8:1, power brakes need a ratio of 4:1.
The MC typically used with the aftermarket boosters lacks residual pressure valves (RPV), with drum brakes you need to add a 10 psi RPV to both the front and rear brake circuits. |
help please.....adding P.B. to drum brakes
