ORIGINAL: leadfootdriver
I had this happen when I started out, hell I was in the middle of a race and my motor screws backed out slightly and then my pinion and spur gear quit making contact and the car just rolled to a stop all slow and I couldnt figure out what happened because, like your chassis the motor was working but the gears wernt touching and I thought I broke it lol
Now that happened to me as well. Embarrassing moments like these makes you double check the screws....