I was trying to put an older set of XT v-brakes on my Cross Check to replace the cantis. When I mount the v-brakes and try to align the pads I can't seem to get them low enough on the rim. Even if I slide them all the way down in the slot after I tighten them the pads still rub the tire a little. I've tried moving the spacers around 100 different ways and nothing seems to help. Any suggestions?