With most dogs, repetition and consistency is the key. Doing things for short spurts won't be as effective as say doing the same thing everyday for 5-10 minutes day.
It can take hundred of repetitions for a dog to learn a trick or habit, some dogs more, some less. Just keep at it and be consistent. I hope he picks up that brushing is a good thing and that there is no need to bite. It's more than likely a defensive bite out of fear, you need to desensitize him to brushing. Maybe giving him treats while you brush so he associates brushing with something good? Don't forget lots of praise when he behaves!
It can take hundred of repetitions for a dog to learn a trick or habit, some dogs more, some less. Just keep at it and be consistent. I hope he picks up that brushing is a good thing and that there is no need to bite. It's more than likely a defensive bite out of fear, you need to desensitize him to brushing. Maybe giving him treats while you brush so he associates brushing with something good? Don't forget lots of praise when he behaves!