I was forced to completely disassemble a duplo locomotive. My son played with it in a sand box and, guess what, it was not working anymore. I used a small brush to clean every single part (mainly axis and gears). I eventually managed to get rid of all the sand. Then I reassembled the locomotive.
I ended up with 2 small parts I could not figure out where to put them, neither what they are used for. Everything seem to work without these 2 parts - my son is happy again. These are curved parts, with a spring attached to it. They are on left part of this picture:
So what are these 2 parts used for, and where should I put them ?