Hy 32Fordpuchoptop and guys, the brake valve in the stock Suburban system is a combination valve as Gord and Fran has said. To cure your rear brake lockup you need to install an adjustable proportioning valve in the line to the rear brakes, it will take some testing and adjustments to get the rear brakes dialed in. If the master cylinder is mounted below the level of the calipers or wheel cylinders, residual pressure valve will be required to prevent "drain back", hope that helps.