There is a shear pin....There is a motor shaft and a mechanism shaft, and a coupling sleeve there will be a shear pin (roll pin) that goes through the coupling and the shaft. You will need a drift to drive out the old broken pin. Also a nail of a similar size will work if a drift pin is unavailable...The roll pin size is approx. 5/32"; but I am not exactly sure.....Its been a few months...I have spares in the 5er at the lake.
When you purchase new pins, the length is not that critical as there is lots of room for it to go all the way through the coupling.
Regards,
John