OH OK, I got ya now, sorry. Ya it's called a slipper gear. ya need to hold that main gear in place and tighten down the purple nut at the end of the spring. I personally tighten mine down all the way. but it's there incase somethign happens to where the wheels stop spinng instantly, like something is jammed in there, it's supposed to keep from shearing off the gears, I think it's a pain in the butt. If you want it to work you need to tighten it down untill it doesn't slip when you take off.