This JK brake master cylinder compensates for the larger caliper piston size with an oversized bore that has 14% more flow to provide greater fluid volume to the front Big Brake Kit. We highly recommend this master cylinder for 2007-2011 JKs with the Big Brake Kit to provide a firm pedal feel. 2012 JKs do not need this kit. Note: Specific steps must be taken when bleeding the brake system, a bench bleed is recommended before installing the master cylinder into the Jeep. Slowly pump the pedal during the bleed process to avoid seal damage.