Hopefully one of you guys might have a clue what's going on here. I ran out of ideas a week ago. I've got a 99 Chevy dually. I did a rear disc brake conversion using the late 70's 3/4 ton 4x4 front rotors and calipers. I got rid of the ABS and used a Willwood proportioning valve. I can barely get pressure to build. I've taken all the calipers off and turned them every which direction and tapped on them with a rubber mallet to make sure all the air is out. I'm getting straight fluid, but still no pedal. I plugged the holes on the master cylinder and it locked up tight, so it's good. The guy at 4wdfactory and another place I called, both said that the factory master cylinder puts out enough fluid for the rear discs and that that's what they always use on the conversions. I don't have any leaks, all the connections are dry. I have no clue what's going on. Anybody got any ideas?