Good luck calling Barton! Pump was manufactured by the American Fire Apparatus company, in battle Creek, Michigan, and went out of business in the '70s, I think. Mr. Milliman is, in that regard, lucky to have a Darley - they're in business as we speak, good company.
Good news is, there were LOADS of these pumps made and sold. Even over-seas. Used on trailer pumps during WWII.
Adam, if you've still got the id tag on the pump, front-side below the discharge valve, you can pull the patent numbers. Then hop over to the US Patent Office web site, plug 'em in, and you should be able to get a copy e-mailed to you. I did this with mine 6 years ago. May cost $10 or 15 bucks. The patent(s) include some diagrams that may be useful.
If the shaft turns until the pump lever is raised, the pump itself is frozen for some reason. Most likely culprit is rust and scale freezing the impeller to the body. Spray the heck out of the impeller and work it back and forth by hand until it loosens up.
If that doesn't do it, you're right, gears may be frozen, and tear-down is indicated.
-Michael
