Overflowing cistern-with no ballcock!?

Sounds like the one I've got with what looks like an upside down can that rides up a ratchet rod and eventually shutting off the water until the next flush.
At the side of this assembly is a long threaded rod down to almost the bottom of the cistern that's the adjustment turn it about four turns then flush the cistern and check level it stops filling at if ok and flushes job done if not continue to adjust.

Charlie
April 2008