UPDATE! I eliminated the rear brake circuit brake bias. I joined the rear lines with a union nut. No more brake bias.
Took it for a drive. Brakes tighten up within 10 minutes. Same as before. At least we know not to blame the brake bias.
My next step is to disconnect the front hard lines from the hoses and check flow back towards the MC. There is only one T junction block in the front circuit.
FYI: I’m using 1/4” hard line from the MC to the brake hoses with a 1/4” to 3/16” adapter nut at the front brake hoses because the hoses only accept that size thread. Most Chevy front disc brake hoses use a 3/16” hard line nut.
