Brake Booster: Application:1964-1972 Pontiac GTO & Lemans. 1964-1972 Olds mobile 442 & Cutlass. 1964-1972 Chevy El Camino & Chevelle. 1964-1972 Buick Skylark. 1970-1972 Chevy Monte Carlo. 1969-1974 Chevy Nova. 1967-1969 Chevy Camaro & Pontiac Firebird. Description:11" GM AC Delco Style Zinc Single Diaphram Brake Booster This booster will work with drum/drum, drum/disk, and disk/disk brake setups. This will power any type of brake system. Firewall brackets are non removeable, they are rivited on.Master Cylinder --Fit most GM application. --Corvette style master cylinder. --Cast iron coated body, dual ball zinc cap --With a 1 1/8" Bore --The cap is attached by 2 small screws --9/16" & 1/2" Ports on Left Side --Will work with any drum/drum, disc/drum or disc/disc setupProportioning Valve:GM brass proportioning valve Disc Drum brake applications.3/8 24 ports for front left and right caliper and 9/16-18 port for the rear brakes 1/2 20" & 7/16 18" portsThis is a good way to properly balance your brake system to ensure sufficient braking pressure.It performs all the necessary functions when using disc brakes in the front and drum brakes in the rear.This valve will reduce braking pressure to the rear when necessary to prevent the brakes from locking up.It also distributes the brake pressure evenly so that the disc brakes are not doing all the work.This valve will also act as residual pressure the rear drum brakes, allowing better responsiveness when the brakes are applied.It also has a brake warning light switch to alert you if there is any failure in the braking system.This valve is a great upgrade over the original and is a must when upgrading from drum to disc brakes.