One of the reasons your buddy gets a little weird when you try to groom him is quite simply that he doesn't like being touched on certain areas of his body. The thing is, it takes a lot of energy to act nervous and stressed, a situation you can do something about by taking him for a nice long walk before you try to groom him.
Choose a room in your house you will always use to groom him and turn it into his personal spa. Add some nice soothing music playing in the background and keep a bowl of treats handy.
Give the space a final magical touch by adding some lavender essential oil to a diffuser and turning it on for a few minutes before you call your pup in. Lavender oil has very soothing properties that will work for your pup just as well as it works for you.
Nothing is more calming to your pup when he is being introduced to a new situation better than the sound of your voice. Keep talking to him using your best soothing voice. Tell him what a good boy he is, anything at all, your voice alone will help to calm him down and keep him there.
The last part of the three Ts method is time. Now that you have Tired him out and Talked to him, you need to spend as much Time as you can touching him and letting him set the pace. Before long he will submit to being groomed with a smile on his face.