Not able to brush my Golden Retriever/Great Pyrenees?

Wait till he's sleepy before you try to brush him and don't freak out. Pretend you're just stroking him and he probably won't notice. When he lays down just start stroking him, and when he's relaxed, just start quietly brushing him. He probably won't even notice you're brushing him. If you still can't get him to let you brush him, then take him to a grooming place and ask them to show you how. Even if they won't teach you then it'll at least get done.