when you bolt on the wheel, where is the rotor going to go? it'll be ok 'till you fix it. get a new bolt and a drill bit that'll fit inside the hex. drill away on the old 1. the head will come off and the remainder is only finger tight. if you leave the bolt out, there will be a new clunk in the rear. the rotor will move back and forth between the hub and wheel as you go reverse to drive. good luck, chuck.