1968 Dart Brake and Booster issues?
I had been told by numerous folks that the larger reservoir on the Disc side of the MC would also be set up to push more fluid to the calipers whereas the smaller wheel cylinders would get less fluid and that the MC would basically be proportioning it at the source and so the D.Block would be adequate.
Not true; BOTH pistons in the M/C are the same size and volume. In a properly working system, whatever you stroke at the pedal, Has the potential to move the same amount of fluid .
The difference in reservoir sizes has exactly one function, to eliminate the constant topping up of the reservoir attached to the harder-working, faster-wearing, front pads which are doing 85% of the work; that is all.
There is NO proportioning in the M/C.
Think about this
the only forces that act on your front calipers to separate them from the disc are; seal-retraction, pad deflection, and disc run-out. As to run-out, there isn't supposed to be any, but loose wheel bearings will always generate some. As to pad deflection, there isn't supposed to be any, but it happens. So that leaves seal retraction as the principal player.
In any case, with all this going on, you might get a piston movement of perhaps .007.
On a pair of 2.5" pistons, this mathes to .0687 cubic inch or ~1.1cc. So when you step on the pedal, and if the pistons are correctly retracted, you can expect ~1.1cc to be pushed down the line. I like a 15/16" bore for this so .0687 cubic inch means the piston has to move .01 inch or a lil less than 1/8th inch . Forget about what you were told; do the math for yourself.
Here's the deal, suppose you go for a year without topping up your reservoir. Suppose that during this time 3/32 orv .09inch of your pad gets worn off. This is ..090/.007 x 1.1cc=~14cc. with your big reservoir, this is a noticeable drop. But with the smaller reservoir, it might be over half empty (I'm guessing). That is why you have a larger reservoir for the fronts.