Tightening up a stretched cable is impossible. If the cable is NOT adjustable to shorten it and make it tighter, then you will need a new one. Here is a link to one. I searched all the parts diagrams in your manual for the cable and find it was NOT listed. I hope this helps as I have researched your problem. Go here:
http://amcpartsstore.com/FSP-Deck-Blade-Engage-Cable-Craftsman/M/B0014G6T1S.htm
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