Drooling normally comes before vomiting or it can occur with a tooth or gum problem.
What breed of dog is this?
What is the age?
Does the dog get any rawhides, bones or dog chews?
There are a couple of things I would worry about and watch for. If there were any raw hides or non food items given recently then I would worry about a blockage of the intestines.
Being a large size dog I would also worry about bloat. This is a twisting of the intestines and can take a dogs life within hours of onset. You will see excessive drooling, nausea, pacing, abdomibal pain and extention, and dry heaving. This is not to be waited out.
Another possibiliy is the dog got into something toxic, even toads can cause excessive drooling and some toads are toxic to dogs. Other toads may not be toxic but will leave a bad taste in the mouth if licked. Try flushing the mouth out with a garden hose, just be sure the water does not go directly down the throat. Check the areas where the dog would frequent and check for anything out of the ordinary tha may cause poisoning.