There are some branches on my sugar maple that are dying. There are no insects that I can see, just some black stuff that looks like mold. The majority of the tree looks healthy. What is causing this and will I loose the whole large tree?
Without seeing the tree, it's impossible to diagnose exactly what the problem might be. Is the black stuff that you mention on the leaves or on the bark of the tree? Sugar maples are somewhat susceptible to verticillium wilt, a systemic fungal disease that plugs their vascular system. There's no specific treatment for the diseases, but often you can keep the tree alive by preventing additional stress. That means watering it during dry periods, possibly aerating the soil in the root zone, and perhaps fertilzing if the tree is not too badly stressed.
However, rather than jumping to the conclusion that your tree has verticillium wilt, it might be a good idea to take a sample to your local cooperative extension office for diagnosis.