Mark IV / Formula 4000 Shortly after the Mark V debuted, the new Mark IV was added as a mid-range packer above the Mark III. It was designed by the same team who invented the Mark V, and both units are described in the same patent, filed in March 1971. The Mark IV differed in that tracks and slides controlled the lower portion of the telescopic packer plate, as opposed to the links used on the Mark V. This packer is still in production as the Heil Formula 4000, the firm's entry-level rear loader. Recently, McNeilus has begun production as the Metro-Pak, most likely under license from Heil. Unit shown here is a Formula 4000 from a 1988 ad. Australian Heil Formula 4000 (courtesy of MitchellM5) 8/3/04 © 2004 Eric Voytko All Rights Reserved Photos from factory brochures/advertisements except as noted Logos shown are the trademarks of respective manufacturers