DONT fill them to the top, it will basicly lock your diff and you will lose the point of having a lighter/heavier oil. Fill them up to just above the cross pins (just over 2 thirds) and then drop a little oil down the slots for the crosspins. There should be no difference in the amount of oil in the diffs, all the same. If you have been filling em 100% STOP NOW because it may really mess with your setup.