Preload on spindle shafts

I am in the process of upgrading my MIll Turn control system. In the process, I am adding encoders to both spindles. I need to remove the nut on the lathe that holds a spacer sleeve. I am going to shorten the sleeve and add a timing pulley to drive the encoder. I am going to do a similar thing to the mill spindle.

Does anyone know how to set the preload on these shafts?

Thanks,