The little bar is there as a spacer, so that when you tighten down on the bearings, they stay a certain distance apart, and dont come together. I dont think it is safe to ride without that bar in there. You should only have to replace one of the bearings to put the bar back in there. Pound one of them out, then put the bar back in, then replace the one bearing you pounded out. If you are careful and remove the one slowly, you might be able to just reuse it until you buy another bearing to replace it.