Campy Nucleon freehub conversion
 

I am trying to convert a Nucleon rear wheel from Campy compatible to Shimano compatible. I have the new HG free hub from Campy and have removed the Campy freehub from the axle assembly. My problem is that the new freehub will not slide on to the axle assembly far enough. There appears to be a sleeve inside the freehub body preventing it from sliding onto the axle all the way. Is this sleeve removable or do I have the wrong freehub body? I seems identical apart from this sleeve.
Thanks for any advice you can give.
Frazer