Along with the 8 purple gear bits and 4 red gears your box comes with 8 high friction washers.  If the gears and gear bits don’t work reliably, it’s probably because there are no high friction washers behind them. Remember that whenever there are two gears connected together, the washers must be placed behind the gears to add a little extra friction. But whenever there are three or more gears connected together, you can leave them off.