Brake pedal going to floor
Hello, I have a 1993 D21 with the RABS system. I recently installed new front rotors, pads and calipers and did a rebleed, after which I lost pressure and haven't been able to get it back despite my best efforts. Since this started I've installed a new MC (which I bench bled), new rear wheel cylinders (because one of the bleeders was all mangled and leaking), and a new section of brake line between the union mounted by the rear diff to the rear passenger wheel cylinder. I also went around to all the unions with soapy water to see if any of them were leaking air and I didn't find anything. After each of the installs I've thoroughly bled the system in hopes that it would be the answer, but so far I've had no luck. Today I was trying to test the RABS actuator to see if maybe it was failing internally and if I should replace it/delete the RABS system entirely. The pedal feels pretty firm with the truck off, but when I turn it on it goes to the floor.
I am kind of lost here, just looking for advice. Thanks in advance.