I'm having a hard time sliding it over the axle into it's place. There is an O-Ring in there if I remove slides in.. but once the O-Ring is set in the hub it won't slide over the initial thick part of the axle. I also recall removing it being difficult I had to tap it out with a rubber mallet (and pretty had too). Any trick on getting this on?

 

i just hit it with a mallet, i'm always a little worried that o ring is gonna pop out of its groove but it always stays put. sometimes ya just gotta use a little force i guess

 

yup use the force! I couldnt get mine off either, and didnt know about that o-ring inside the brake hub! Just rotate it 5-10* per hit, and keep at it until it pops off!