Uncle Fuzzy: Instead of just wondering about the integrity of the 30+ year old cables why not put a new set in? It's not that complicated or expensive a job. With lots of gliders there is a calendar or flight hour limit on the cables anyways.

I recall Derek Piggott writing that the DG-100 rudder locks over and that the Janus does too so a Janus flight was a good way of experiencing the effect with an instructor if you had purchased or were considering purchasing a 100.

My 15B slips very steeply and effectively and behaves well in a full slip but the incident with the JS-1 also had me wondering about what would happen if a cable broke. When I disconnected the left cable at the turnbuckle aft of the pedals in the process of replacing my cables I noticed that the rudder was only deflected about ten degrees by the spring on the side that was still hooked up. Of course this doesn't tell me what it would do with a 50 knot or more airflow over it. Since I frequently fly barefoot I suppose I could do a test in flight by simply grabbing one pedal with my toes and pulling it backwards putting slack in the cable while not touching the other pedal.