Thanks to all respondents. I couldn't find it in any of the literature. Here’s the deal: on the road or in the garage, initial brake pedal travel is long, second pump comes up solid. Next few pumps always solid. Wait awhile, long pedal again. M/C pushrod is adjusted for minimum play. In the past few years, I’ve swapped Girling master cylinders (both .7” and .75”), rebuilt calipers at least twice, tried both .75” and .7” Girling rear cylinders, alternated DOT4 and DOT5 fluids (flushed each time), used the OEM Residual Pressure Valve, no RPV, Wilwood 2 psi RPV, Wilwood 10 psi RPV. Have always pressure bled. Replaced pads and shoes, replaced hoses (AN-3 braided stainless/Teflon). Brake lines from m/c to each wheel are 3/16”, 1/4” from reservoir to m/c. No leaks. Strangest thing - if I plug the line to the rears and bleed, leaving front calipers enabled, pedal is always solid. Likewise, if I plug the hoses to front calipers and bleed, leaving rears enabled, pedal is again solid. It’s as if the m/c piston can’t move adequate fluid to the four wheel cylinders on the first stroke. If air is being drawn in, I can’t find it. Thought that my skimmed OEM rotors may be too thin allowing excessive caliper piston travel. I'm grasping at straws here, admittedly. Pressing on, regardless…
Apology for the long post.
Ted