Wilwood's new Combination Proportioning Valve substantially simplifies mounting, plumbing, wiring and brake proportioning adjustments. The combination block maintains full isolation between front and rear fluid circuits and can be used in conjunction with any tandem outlet or dual mount master cylinder assemblies. Wilwood's new Combination Proportioning Valve substantially simplifies mounting, plumbing, wiring and brake proportioning adjustments on vehicles with custom brake systems. The combination block maintains full isolation between front and rear fluid circuits and can be used in conjunction with any tandem outlet or dual mount master cylinder assemblies. The rear circuit has a single inlet and single outlet with the adjustable proportioning valve. The front circuit has a single inlet with two outlets. It can be run as a single outlet with one outlet plugged, or used to split the plumbing on its way to the front calipers.