Let me add to Mike's description.  While you have the arm off, get a pin or
small nail and scrape clean the grooves on the shaft.  I found that mine were
packed full of scrapings (from the arm), and I think just tightening it would
not be effective.  Once they are clean they can bite deeply into the arm,
like they did at the factory.  Now they are tight and powerful.

Bill Marshall
'85 GL Tiico "Pandora"
Aurora, IL