When I bake a cake, it looks fine and as it should be, until I turn it out on the cooling rack. Then I have a problem with the cake cracking....I know I can still use it, with the help of enough frosting. But what am I doing wrong? Am I baking it too long? Not long enough? Should I level it before I turn out on the cooling rack? Any thoughts appreciated

If it has a large hump, then yes, you should cut that off before you turn the cake out of the pan. You should let the cake cool at least 10 minutes before turning out. Once you've turned it out onto the rack, place another rack on the flat side of the cake and turn it again. That way, it will cool right side up and not on the hump.

Follow Diane's suggestion, most likely is your cake has a fine crumb and a large hump; then when lying on an unleveled surface makes it crack.

You can also try to prevent the hump... the use of flower nails and baking strips will definitively help t get flatter tops.