A-Team Performance Master Cylinder 4-Port Corvette Style GM Disc/Drum Proportioning Valve + Lines This is a 4-Port Corvette Style master cylinder, DISC/DRUM Proportioning Valve, bottom mount bracket, and the brake lines to hook the Proportioning Valve to the Master Cylinder. This kit is for Disc/Drum applications. The Master Cylinder is used for 4-wheel disc or drum brakes 1 inch Bore Master Cylinder. A Disc Brake Combination Valve is a Necessity When You Are Doing a Drum to Disc Conversion