23. For safety and convenience, we’re also replacing the single master cylinder with a dual master cylinder and power booster. Here, Gil begins the swap by using a 1/2-inch tubing wrench to disconnect the line from the original single reservoir master cylinder. A 9⁄16-inch box end wrench is used at the power booster. The factory drum brake power booster cannot be used with a dual brake system master cylinder because it won’t clear the shock tower.