Brake service will also include a check of your brake fluid. When the brakes are applied, the pressure in the fluid actives the brake pads or shoes. Not enough fluid means not enough pressure to brake properly. Also, water builds up in the brake fluid over time, which leads to corrosion, leaks and brake damage, and with hard use, the brakes could severely fade or even fail. You should change the brake fluid when your manufacturer recommends to avoid these problems.