Speedo gear question

[69GWC]

I do not have a speedo on my truck it seems the gear in the TC (221) just free spins rather then turning the cable (cable is fine and will spin the speedo with a drill on it), well i took the output cover off and the gear just sets on the shaft with no type of "key" way or anything to keep it in place.
My question is this, is this a compression fit and will taking out a shim hold it in place or am i just going to increase bearing preload.

hope that makes since as there has to be something that holds this gear in place.

thanks for any help