After amking three or four disks, I now get an I/O error on the //c. it will not read or write any disks at all. I have read that this *could* be caused by an erratic disk drive speed.

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It could, but is more likely to be a dirty read/write head. Testing the drive speed involves getting a testing program to read from disk (kind of chicken-egg situation for you now), or roughly with a fluorescent light. So I'd start with the head. Take the IIc apart, remove the top of the drive, and gently lift the pressure pad arm up - it won't lift up 90 degrees, so feel for where it wants to stop. Wipe the ceramic head (it's the white bit under the arm you're lifting) with a Qtip lightly dipped in isopropyl alcohol. Rub with one side of the Qtip, dry it with the other, and let it sit for a bit. Then retry saving disks - but be careful reusing old ones. That might be what fouled your head in the first place.