I have stumbled into a brake issue after other parts replacement. I changed the 4wd solenoid 2 weeks ago, still had grinding noise. So this week took hubs etc off, hubs and actuators were finished. Today reinstalled new hubs, new actuators, tie rods, and the calipers. I removed calipers 2 days ago and got new ones. Left lines dangling fluid slowly dripping. Had to wait to install as I was painting the knuckles etc to prevent rust issues again. So the lines sat open for a day, figured ok as was going to do a fluid change at all 4 wheels anyways. Bleed the brakes and that's where my issue is. With engine off, I can get some pressure to build but as soon as truck starts pedal goes to floor. That tells me booster is fine. I have bleed each wheel many times, 2 large bottles of fluid. Each wheel has good flow of clean fluid. I don't believe the master cylinder went out after doing this simple caliper change, no brake issues before, just replacing the rusty calipers while I did hubs. When bleeding, pedal is kind of stiff and feels like bleeding operation is working. Soon as truck starts, it's all gone. I've been doing bleed as LF, RF, LR, RR. In morning I will do LF, RR, RF, LR cross bleed to see if any help.

Is it possible I introduced air into the ABS module and it is trapped? I'm at a loss as to what could be giving me the issue. Truck has been fine for years so it would seem strange to have a booster or master cylinder issue after changing front calipers.

Any insight or direction would be helpful.