The ability of the Nissan disc brake pads to produce friction on a metal component without causing damage to it is the reason this special material is used in your braking system. The material the disc brakes pads are made out of is designed to disintegrate slowly over time as friction is being created. The end result is this material turns to dust. When friction is created by forcing the disc brake pads against the rotor, an intense amount of heat is also produced on your Nissan brakes. It is this combination of friction and heat that in time will wear out the Nissan disc brakes pads on your vehicle; requiring them to be in need of replacement. The only involvement of the hydraulic system has when the disc brake pads are being replaced is the repositioning of the brake caliper piston. This piston has to be moved back into the caliper so they will be enough space for the new pads to be fitted into the caliper around the brake rotor. This will then raise the brake fluid level in the brake master cylinder. If brake fluid was added to the master cylinder's reservoir by the owner thinking it was just low, then brake fluid will leak over the sides and has to be cleaned up so the paint on your Nissan will not be damaged. Because the replacement of the disc brake pads does not open the hydraulic brake system on your Nissan, the brake lines and components do not have to be bled of any trapped air since there should not be any. With the wheels back on the vehicle it is then ready for the road with full braking potential at the disposal of the driver.