Some steps to a lighter brake pedal

Question:

I set up my 1941 Chevy coupe with rack and pinion steering and 11” disc brakes, with a 1955 Chevy drum brake rear. I decided to go without a power booster and used a TCI under floor bracket with a new dual chamber master cylinder with large bore (the master cylinder bore is about 1.250”). The result has been a very hard pedal. I really have to stand on it to stop very fast.

Should I have gone with a smaller bore master cylinder or will I need a booster? Also, will adjustment of the proportioning valve help?

Answer:

The bore in your master cylinder is too large. With a manual brake system the master cylinder bore should be no larger than 1-inch in diameter.

Change the master cylinder and evaluate how much pedal effort is required to stop the car. It will surely be noticeably better but if the pedal is still too hard there are additional things you can do.

Adding a power booster will definitely reduce the pedal effort.

Changing the geometry of the pedal linkage will also help. A good rule of thumb is that a pedal ratio of at least 6:1 is required for sufficient leverage. The ratio is calculated by measuring the distance from the pedal pivot point to the point on the pedal where the master cylinder actuator rod mounts; measuring the distance from the pedal pivot point to the point on the pedal where you apply the force to actuate the master cylinder (the point where your foot contacts the pedal), and dividing the latter by the former.