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the adjustment was wrong and it ran too close to the spokes and got tangled when I changed to the largest cog. The Simplex Tour de France works on a spring loaded plunger and has no limit screws and I had allowed too much adjustment....I think the rim can be saved so will have to save up to get it sorted as I just splurged on 3 entire wheel rebuilds the other day...
jeff80-
This was an all too well known failure back in the day.
It was usually caused by the arm of the mecahism getting bent (often by someone other than the owner!), but faulty adjustment was certainly another cause. Benelux and Huret were just as bad, and this problem was perhaps the main thing which made the Campag Gran Sport such a revelation. With a Campag, if someone knocked your bike over it would only push the mech over against the spring - as soon as you picked it up it just sprang back to where it was before with no harm done.
In this case, I note that the block is very close to the hub flange, which meant there was no margin of error to avoid this disaster - a spacer (or two) behind that block might have secured a longer life for the unfortunate TdF mech.
clubman
Ah no, did the derailleur let go or something? The rim should pull straight again. Fingers crossed.