Over time, curtain cords can become stretched, frayed or dingy, compromising their ability to function properly. Replace your old cord with a new one to restore the overall performance of your curtains. Curtain tracks work on a pulley system, and with knowledge of the correct path that a cord has to travel through this system, the new cord can be easily installed. To work on your curtain track, detach the track from the wall, remove the curtains from the curtain slides, and place it upside down on a flat surface.