If I understand your problem correctly - you are experiencing rope breaks
at the point where the rope enters the weaklink piece - but the knot is
not slipping.

We use two of these systems on PA-25s and have not had that problem -
although we have had other problems. You might check inside the black
cone on the tail of the plane and see if there is some sharp edge that is
chaffing or abrading the rope there.

We use Tim's Dacron rope and we replace it frequently. Before that we had
a problem with the knot slipping. We still have a problem with the rope
snarling on the reel occasionally and not playing out competely - which is
very dangerous becuase the reel is not designed to take the towing load.

I'm not a big fan of the system - it just replaces one set of problems
with another.

Roy B.
Greater Boston Soaring Club