looks like i need to replace my rear wheel cylinders. what difference can i expect if it choose cylinders with a smaller bore. could it make the pedal firmer? or would it be a negative effect?

Smaller cylinders will transmit less force to the brake shoes.

If you have a rear lockup problem, this is what you want to do.


Pedal won't feel firmer, but will have less travel because you don't need as much fluid to extend each wheel cylinder.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

i have a recipe i followed to put disc brakes on the front of an A108 van. at the time i also upgraded the rear drums to 11"ers. i have an inconsistent pedal height. i need to double and triple pump about 50% of the time. the front disc are always perfect when i bleed the system. the rears always seem to have air in them. i find no leaks anywhere. i am wondering if the rear wheel cylinders need to move more fluid thnt the MC this recipe called for can move.

The problem with your rears is likely that there is no anti-flowback check valve in the MC section for the rears. Wheel cylinder pistons tend to get pushed back too much by the springs as your ride along, and need this check valve in the MC feeding them to keep the fluid from gradually flowing back into the MC. If that happens, then one stroke of the MC will not move the wheel cylinder pistons far enough and you will have to double pump. The air may be being drawn in by this around the pistons seals when they retract due to this.