Based on our shop experience specializing in heavy-duty brakes since 1985:

• Bench Bleeding: Never skip bench bleeding the master cylinder assembly on a vice before mounting to the firewall or booster face. Trapped air pockets inside the bores create persistent spongey pedal issues.
• Proportioning Valve Setup: Always configure the external proportioning distribution block properly to regulate fluid balance pressures between front and rear circuit lines.
• Fluid Compatibility: Use clean DOT 3 or DOT 4 brake fluid only.