[Bob Putnam]

We also use a 7/8" and 3/4" setup. The front wheel cylinder size is much larger for our front calipers than the rear - requiring more volume. Our balance is still about 70% effort to the front.

The 5/8" cylinder will require almost twice the travel as the 7/8" for the same fluid volume. If the original design was approximately right, you simply don't have enough fluid volume to bleed the brakes. Not to mention, you might as well disconnect the rear brakes. They're not doing much anymore.