Make it go real fast....

The gears use centrifical force to shift. So once you get going fast enough they'll automatically shift into second. When you slow back down first will automatically kick back in. You'll know that it shifted because you'll hear the engines rpms drop just like in a real car. There's also a way to adjust for the shift point, incase you want second to engage earlier or later. I'll try to get some pictures posted later to show you what to mess with.