SPeedometer issue!

my speedometer dont work, i turned it by hand and my brother looked inside and told me that it jumps, means that the cable and the meter s ok, i took out the small plastic gear at the end of the gearbox (it was violet) adn it was ok as i guess but b4 taking the gear out i turned it with a screw driver and it was free!?

i had the plastic gear in my hand, and it was pretty fine, the teeth were good.. but i stuck my had in the hole where the gear goes in i was surprize that there wasn't nthing that could drive the gear! is it possible? could that part be fixed by not removing all parts in the gearbox?