MBM PVKS-4 - GM Side Mount Brass Proportioning Valve Kit for Disc/Disc Brakes Kit for Disc/Disc; For use with 9/16" 1/2" Ports; Left Mount Brass Proportioning Valve, Steel Lines, Bracket and Proportioning Valve Plug Left side means drivers side AC DELCO style proportioning-combination valve in brass. carry individual proportioning valves for ycustomized application. These combination-proportioning valves are based on the popular AC DELCO 172-1353 (disc-drum) and 172-1361 (disc-disc) valves. When upgrading your vehicle from drum to disc, these small items are a must. These components ensure proper fluid transfer and contain a residual pressure valve for proper braking feel. These valves contain a low pressure shut off valve and warning light switch to ensure driver and vehicle safety should your brake system lose hydraulic line pressure. Aftermarket imported master cylinders with built in adjustable proportioning valves DO NOT feature this and could put you and your vehicle at risk. Includes: