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Oi.

Drum cylinders and disc calipers work on the same exact hydraulic principle. To move the larger piston outward (any distance) is going to require more fluid than moving the smaller piston.

Can I say duh now? :)
 

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6869704x4 said:
....The difference, I believe, is in in the travel of the pistons. The caliper piston moves very little, unless you have some serious rotor warpage, in comparison to the drum pistons.........
What makes you think that? A properly installed drum brake shoe should be turned to match the drum radius perfectly and when properly adjusted will have much the same tolerance in it's fit as a rotor/pad.

edit: Editing myself? Jesus.

To elaborate further, to move a piston that has twice the face area of another requires twice the fluid volume to move it the same distance.

So if we say that the caliper piston is 2" dia and the wheel cylinder pistons are .5" dia each (x2) to move them the same distance will require that the 2" piston have twice the volume of fluid as the 1" (.5 x 2) wheel cylinder pistons.

I'm sure this is no news to you. And it's a very simplified scenario. As for the M/C in the equation, a smaller bore M/C will work as long as it has enough travel in it's stroke to provide the necessary volume of fluid movement needed. When you upgrade to rear discs using a much larger piston bore you need to upgrade the M/C bore (or travel) as well.
 
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