Hmmmm.... I'm not understanding what's wrong with it. The needle spins around like a second hand on a clock? I doubt if the "gearbox" is broke, cause that's down on your front axle tucked inbehind your front fork. Sounds like all your damage was up at the speedo/handlebars. Someone recently posted about a guy that does professional style speedometer restos...(1DeadPrez and someone else???) They should be able oto hook you up. You can buy a OEM NOS one still from HONDA but it is chrome/red and doesn't say ATC on the inside.
Bruce
'85 ATC350X - "Showgirl" '86 OEM plastics/Fork boots, Rear Axle/Rotor/Hubs, Hondaline Fender stabalizer/extender, Speedo/Tach, Tank cover.
'86 ATC350X - 'Go-Go Girl'
'82 ATC250R - 'California Girl' - Progressive springs F and R, Hondaline HL Guard, Fairing and Speedometer.
'82 ATC250R -'Snow Bunny' Ice Racer, Very Clean, Hondaline Fairing, custom FT tire, will put in the 300R motor
'70 US90 'Ol'Girl" - Aquarius Blue... all original seat and tires. Resto project in the future
'85 ATC250ES-'Workin' Girl' CMP Footguard, Hondaline Mudflaps, Speedo, HL Lens, Block Heater, Work Light, Foot Peg Covers and Cooler Rack
'85 ATC70 - All Original
'84 Yamaha 225DX - Durablue +3" axle, DR motor, New Plastics, Foot, Hand and HL Guards.
'85 Yamahauler - Gun Rack & 'Nerf Bars'
'85 Yamahauler - Nearly together and restored
'83 Suzuki ALT125 - Pieces
'89 Suzuki LT-4WD - Token Golf Cart