these shims, exactly where do they go?

My daughters SC10 is doing that click click click sound, but when I took apart the gear diff, the only shims I saw were under the sun gears (the bigger internal gears, 2 of them) under the pin. On my 1/8 scales usually see a shim behind each of the smaller gears as well or at least we put those there when converting old rc8s to electric.