Richard
I had a look at what should happen when you bring the parallelogram down from the upper position:
1. first the bellows is totally folded
2. with the 100mm in position, the bellows begins to drop right away and gradually. When the parallelogram is almost down (plus minus 80 percent) it drops the last bit in one go. Do not worry if yours doesn't do that final drop, it just means it could use to be serviced. But if you need it to go down the final bit, you can push or pull it down. Its drop from being closed is about 7,5cm
3. with the 60mm in position, the bellows begins to drop right away and gradually. But not as far down as it does with the 100mm in place. Its drop is about 4cm.
I took away the Bowden cable: with the 100mm in position there is no difference when bringing the parallelogram down. However, with the 60mm installed the drop is like with the 100mm. Which will be the reason behind your problem.
Then I did what you have in mind, using a small hex key I pushed the 'wheel' out. But it comes right back in when I took out the hex key. Also, it landed against the lower cam, not on it.
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The cable works perfectly. But it is the weak parameter of the IIc. As said before, when moving the slider without lifting as indicated, the wheel lands against the cam. That causes strain to the cable and is the reason why these cables break. I had that once about 30 years ago, then a Leitz repairer explained this to me and all is okay since.