Gentlemen,
I got the effin' brake system fixed! (must have been the beer cans hurled at her last night). I now have 100% pedal, a better pedal in fact than I've had since I've owned her. The pedal is nice and high, with only 1/2" of travel before they start stoppin'.
Here's how I fixed it (long explanation but worth the read in my opinion). My theorey on what grenaded and caused this whole mess follows.
Last time I left her, I had replaced the master cylinder, power booster, ABS hydraulics, and took apart and cleaned the combination valve. Total of 1 gallon of brake fluid vacuum bled thru the system (bench bled the master, bled the new ABS hydraulics, and bled her at all four corners). Still had a low pedal, about 5% brakes, brake light stayed on. Zero pressure to the rear brakes.
So tonite I went out and clamped off the rear flex hose. Mashed the pedal a few times with the key off, turned the key on, and the light was off. Mashed the pedal like a madman with the key on, engine off, no brake light. Fired her up and mashed like a crazy bastard, no light. Pedal felt pretty good. Shut her off.
Took the clamp off the rears, repeated above. Light stayed on and pedal felt like crap. Put the clamp back on, mashed the pedal a few times, key on, no brake light and the pedal felt good. Removed the clamp and cracked both bleeders at the rear end. LR spewed air for 5 seconds (I had already vacuum bled over a quart from this line) and then started dripping. RR spewed nothing but air for 45 seconds (had also bled over a quart from this line) and then started dripping.
I let the rears gravity bleed for an hour, having to refill the master cylinder once. Tightened up the bleeders, fired her up and viola, problem solved. Weird huh?
Here's my theory. Either the master cylinder or ABS hydraulic module took a dump last Friday and threw the proportioning valve off center. I couldn't tell you which one of these it was as I replaced both with no effect. But I know it was one of them. Anywho, I bled 1.5 gallons of brake fluid thru the system (gravity, vacuum and pump and squirt methods) over the weekend, but somehow, somewhere there was an assload of air trapped in the rear system. Where it came from we'll never know. I am truly baffled there was that much air in the system after bleeding that much fluid thru. This trapped air prevented pressure from building in the rear system hence preventing the proportioning valve from recentering itself and keeping the brakes nice and shitty.
For some reason or another, the combination of things I did tonite got the air unstuck and I was able to get it all out. I still can't believe it.
I'm leaving her sit overnight, taking my wife's truck to work tomorrow and am going to bleed anouther quart through her tomorrow night just to make sure I got it all out. The ABS module is still sitting in the bed of my El Camino (aka "workbench") as I had to remove it to get the back plug of the combination valve back in; I'm afraid to hook it back up!
Thanks to everyone for your willingness to lend a few brain cells in my direction. It is very much appreciated.
Regards,
Doc