Rear discs won’t lock up after frame off build

[z71se]

Hey guys I have an issue that is just really stumping me. I’m using a 4-wheel Wilwood kit completely spec’d by them for 15” wheels. I plumbed the whole truck with 3/16” line and there are no leaks or air bubbles coming from any of the fittings or bleeder screws.l anywhere in the system. The master(s) I’ve tried have been bench bled correctly and fluid volume is clear and without bubbles. I’m running a Wilwood “combo” splitter/ adjustable proportioning valve and I’ve tried adjusting the bias every which way... makes no difference to the rear lockup problem. With the rear axle lifted, and the truck in drive or reverse, I can slow the rear wheels a little but I can’t bring them to a complete stop. I haven’t driven it yet because I’m sure the truck would lurch forward and might be unstoppable given the inability of the rear brakes to stop the truck.

I’ve tried both a stock replacement 1.125” master as well as a C3 Corvette disc/disc 1.125” master (the bore size that Wilwood recommends for my calipers). Both had identical results. I don’t think the master nor bleeding is the issue because two OEM masters had identical results. Could the problem be that I’m using 3/16” lines with these two OEM masters? Obviously the C10s had 1/4” rear lines but I’m not sure what C3 Corvettes had. I’d like to avoid spending $300 on a Wilwood master if it’s unnecessary. They’re gawdy and stick out in the engine bay.