I used the Bruder axle cut down leaving a stub in each wheel. Then made my own floating axle and spindles. The stubs of the Bruder axle pass through each spindle and then a washer is welded to the inside to prevent it from coming out. A little bit of lubricant on the axles and they turn easily with the light weight of this model. I'm sure there is a better way of doing this but it was very quick, easy and cheap for me to do it this way.
Reg