Just wanted to update the bunch of folks who gave so much useful help with my brake problems. The original problem was too much pedal force required for too little braking, with the pedal getting a little too close to the floor for comfort. None of the symptoms jumped out at you. Rather, things just weren't quite right.

So... I diagnosed the issue as a bad master cylinder and replaced it. A month of travail ensued. Couldn't get a firm pedal to save my soul. An oddity, to me at least, is the brakes would not pump up, which I have always considered a characteristic of air in the system.

You can read all about it at the following:
http://www.brickboard.com/RWD/index.htm?id=914021&show_all=1
http://www.brickboard.com/RWD/index.htm?id=925759&show_all=1

The short version is that I ran more than 2 gallons of DOT 4 through my brake system. I pumped. I sucked. I blew, and every combination of all three. I tried unprintable incantations and said to myself many times during all this, there cannot be one damned molecule of air left in there.

Ultimately, I began to listen to what I was saying. If there can't be any air in there, the problem isn't air. I had already taken what I thought was a close look at the calipers for any lost motion between pistons, pads, and rotors. Found and replaced one faulty caliper, with no effect. Checked that idea off the list of possibilities and kept scratching my head.

It wasn't till (much) later that I noticed a fair amount of motion in the front left caliper while standing next to the car and stretching a leg in to press on the pedal and staring at the pads. Estimated I was seeing maybe 0.030" of squeeze, just on the lower pistons, when I pressed on the pedal. It would immediately relax when I let up. Hmm...

Some rough calculations suggested this "small" motion on the four lower pistons would translate to something approaching a 1/2" of travel at the master cylinder, five times that at the pedal. That's just the amount of "sponginess" I was experiencing.

I theorized that the upper pistons were sticking a bit, for whatever reason, and as a result had worn the pads convex by extended dragging during delayed retraction (actually, the original theory was the opposite of this, but as it underwent revisions while I lay awake at night...). Then, upon pressing the pedal, the whole pad had to flex to lay down flat on the rotor.

This would explain why they wouldn't pump up. The pad acted as a spring that quickly returned the more freely moving lower pistons whenever pedal pressure was relaxed.

How to test the hypothesis?

The easiest (and cheapest) test I could contrive was to replace the pads with new presumably flat ones, although they only showed about 25% wear. Sob. Unfortunately I did not have a spare set so there was a delay in stocking up.

When I finally got to it I was amazed how much effort it took to pull the pads. Even more amazing was how oddly worn they were. Every edge was non parallel to the pad backing plate except for the rear edge, the only one you can see when they're in the caliper (naturally!). I found a pretty substantial build up of I don't know what, rust?, brake dust aggregate?, where the top of the pad is supported inside the caliper, closest to the center of the rotors.

This buildup was tenacious enough to greatly resist my efforts to remove the pads (not to mention the buildup). It also greatly resisted the upper piston's efforts to apply the pads to the rotors. I usually scratch all that stuff down to the casting swapping pads. Did I miss it? Did it accrete in the mean time? All I know is it was impossible to install the new pads with it there. Scraped and scraped till everything moved freely.

Ultimately, I think a number of issues contributed. The car is my winter car (you can tell because I'm working on it in the winter). Hence it sits all summer. I try to drive it now and then, but... The lower pistons were returning hard when I first tried to pull the pads, no doubt gummed up seals. The tops of the pads could not move correctly because they were trapped in whatever it was. The combined effect was greatly uneven wear on the pads which were flexing and pivoting when the brakes were applied.

Replacing the pads immediately resulted in much firmer pedal. Over the course of driving to work for a couple of days, 44 mile round trip each day, the pads fit better and better until I now have pretty good brakes again. Not perfect - the calipers are definitely scheduled for replacement - but good enough for a guy who's been pumping brakes and smelling DOT 4 in his sleep!

FYI and thanks to all who provided help and moral support. Hope to return the favor.

Chuck