When you put modern front disc brakes on your 55-57 Compatible with Chevy car, you should update the master cylinder as well. The stock 55-57 drum brake master cylinder does not have the capacity to supply the proper amount of pressure for front disc brakes. This simple bolt-on power brake assembly will ensure your brakes are operating at peak performance. Kit contains a 1" bore master cylinder with 1/2"-20 and 9/16"-18 outlets, 8" dual diaphragm booster, and a disc/drum combination valve (provides proportioning and metering). Also includes line to connect the prop/metering block to the master cylinder and the necessary hardware to mount the booster to your original 55-57 Compatible with Chevy brake pedal. Measures 14-1/4" from firewall bracket to end of master cylinder. Includes proportioning/metering valve. Learn more about selecting the proper master cylinder for your vehicle by reading our tech article. Brake System Selection. Installation Instructions