The procedure I used w/ the Scott diaphram cylinders was to add fluid from the bottom (brake bleeder at the wheel, if you have one) until the cylinder resevioirs were full (w/ the filler plug removed), then disconnect the linkage from the front heel pedals so that you can pull the brake cylinder lever to the maximum aft travel. While holding it back, top off the reservoir w/ 5606 and replace the filler plug before releasing. It helped some, but the ultimate fix was installing 6" Clevelands and the ???River brake boosters. I had already installed the Clevelands before the brake boosters, so don't know first hand how well the boosters w/ work w/ the old expander tube brakes. My understanding is that the old Scott diaphrams are a "low pressure, high volume" system as opposed to the Brake Boosters which are a "high pressure, low volume" system which is more suited to the requirements for disk type brakes.
Hope this helps,
3719Mikey