My little brother has ADHD and a form of autism. It's very, very difficult to teach them discipline. There are times where he does it just out of defiance. It's obvious. There are other times he does it because he just doesn't know better or can't help it. There are times when I can't handle him and have to take him home. There are other times that he's just good as can be.
The only thing I can offer that I have found is : CONSTANT STRUCTURE & DISCIPLINE.
It helps soooo much when he has a schedule to follow. If he has the exact same things to do every day, it's amazing how much better he behaves. He always has to be doing something as his mind runs a hundred miles an hour. But if he knows what he's supposed to do, he just goes thru the motions. The more I can keep him busy on a schedule, the better.
And you just have to know that 100% of your time will be dedicated to disciplining him. If I let him get away with anything "just once" - that's the end of it. The rest of the day is shot & I can give up hope of him listening. It's hard b/c you want to see him have fun and you feel sorry for him. But it's really better for him in the long run.
He may not have fear, but he has wants and the desire to be awarded and congratulated. If I tell him to go get a cup of juice and he does it correctly - I tell him that he did a great job, what a big help, thank you, thank you. If I tell him to wash his hands - I tell him how awesome it is that he did that with no problems and hung up the towel afterwards. He loves the praise and is then so willing and eager to please.
I would check into local support groups for ADHD. Talk to other parents and see what works for them.
Good luck.