Suggestion on the thread to park at the bottom of Rails Rd, next to the river, to the usual footpath up to the crag.
Its just under a mile along the A57 (which has a pavement) to the dam and marked on the OS map at SK291873.
Or using the Google map you can find it at: 9CJP+JJM Sheffield, in the little triangle between Manchester Road, Rails Road and Rivelin Valley Road.