The old minivans had a prop valve mounted at the rear, attached to the rear axle with a link. As the rear suspension was loaded heavier or lighter, it would adjust the valve which would increase or decrease rear brake bias.

Once you modify your car from OE, bigger or smaller tire, different brake kit, lighter weight or substantially different weight bias, etc., the OE calibrations go out the window. With any major modification and/or replumbing, the OE prop valves, distribution/compensation blocks, etc., hit the can. I don't care if they are a dime a dozen, I won't use an auto part store master if I don't know all about it. Even an oval track and a drag car system and hardware are completely different. Drag race cars need parts designed and configured for drag racing. Just like the parts that make up an engine - if the brake system is a collection of stuff from different manufacturers, picked out of a catalog based on price or bad information, mis-matched, sized wrong, being used for the wrong application, or OE crap being used for something it wasn't intended, it won't work right.