If the cord is nylon, find an end (either the snapped end or one at the master carrier) trim the end with scissors, burn with a lighter and melt the new cord onto the old, trim the join so it is tidy and wont snag and then gently pull the cord through the system until you are back to the beginning. A system with a continuous looped cord has 2 knots on the master carrier, a system with pull weights is simply looped around all the pulleys.
Steve, October 2010
