AJ, overall good work. I came up with 2cc's front and 3 cc's rear with a given set of what I think are good assumptions for the fluid into discs and cylinders; I used more seal retraction with a single piston system, 1" wheel cylinders and a tad less wheel cylinder travel. So the same ball park. But, change the assumptions a modest amount, and your or my results for the capacity needed can reverse, with discs needing more than drums. All the numbers we have used are grabbed from the air and not measured. It is too much of a stretch to make any hard conclusions for all situations from such numbers.
If I have it right, the MC piston for the front brakes has to push the distance that pushes the fluid needed for both front and rears. If I read your work right, you used only the front caliper volume to work out the MC stroke. Please check me out, but I think that yields a 4:1 error in the fluid movement portion of your MC stroke computation if one uses your 3x larger wheel cylinder fluid volumes. And it may have to push even more stroke to get the comp port on the rear chamber covered too if it closes later than the front port to possibly add more MC stroke. (I have no clue about the sequence of comp port closures however.)
There is only one C-port. The rear chamber gets its fluid by bypassing the one-way valve in the center of the piston stack.
And from direct experience with going from rubber lines to stainless braided lines, I can honestly say that the amount of fluid needed due to line expansion can be quite large. Just from the sensed pedal movement changes in those cases, it can be as large than the caliper and wheel cylinder fluid capacity for moderate to hard braking (like racing).
Once the C-port is passed, no more fluid can enter the line. If hose flex is excessive, it shows up as a longer piston stroke and subsequent pedal-travel, and a springy feel. Since we are only using 1/4 of the piston travel to set the pads onto the rotor, we still have3/4 of the stroke available for system flex.Thats why there is six or more inches of total pedal travel available. Well that and for compensation to poorly adjusted drums.
Teflon lines reduce/eliminate a lot of system flex, and give my ride a nice confidence-inspiring, hard-pedal. .
BTW, I don't think anyone one said that a drum/drum MC wouldn't work a disc/drum setup. Re-check the postings above. (And I did not go back and change a word.) I did say that there was a case for disc/disc where a larger MC bore fixed the problems and provided the link to that. The point was to try to give the OP a head's up on this potential issue as he looks at rear discs.
This comment is not related to this thread, but rather to all the posts of bygone-days.
The older , short height, small reservoir MC's for drum/drum don't have the capacity to keep filling the space behind the caliper pistons as the pads wear, but as you say, that only has to do with long term wear, not for an individual braking stroke.
that is correct.
I would not use just any old M/C for road-racing, or autoxing. But for a summer-only streeter? How many miles does a streeter put on in a summer, and what percentage of those are pad-wearing miles? I have a M/T with plenty of compression braking. I drive defensively,cuz I wanna drive my car all summer;not have it in the bodyshop for weeks to months. I pick my times and spots where Ima gonna get stupid. I have had O/D, almost since day-1. What Ima getting at, is I use my brakes very little. Subsequently, my pads last a looong time. Some might say I drive like a grampa. My brake system has accumulated 125,000 miles on it since year 1999. I won't tell you that I'm still on the first set of pads, or that I have never had to add fluid. That would be preposterous. lol
And let me bold a few words too.... a few words