I had a foster dog - 1 yr old - who was raised in isolation and had never seen anything! She was terrified of everything - parked cars, mailboxes, rocking chairs - you name it.
Get a small bag full of hot dogs, cut into tiny pieces, or anything that your dog absolutely LOVES. Do not give him this treat at any other time - only during desensitization. And do not ever soothe or comfort him when he is being fearful - dogs see that as praise - i.e. "Oh Good boy - you're acting afraid". Ignore his fear.
Take your dog out in the driveway, if you have a car parked there. If not, go to a place where there are parked cars. STop walking towards the cars before your dog shows any fear. Have him sit, and give him a treat. Then go home. The next time, go a little closer and so on.
If he only fears moving vehicles, do the same thing - go on the street, but stop before he is afraid. Have him do obedience exercises - sit, down, etc. Ignore fear, and give treats for not being afraid.
If you have a friend with a car, ask him to drive past your place while you are outside with your dog. Get your dog as close to the street (and the car) as you can without him being afraid. As your friend drives by, toss a treat a foot or so in front of you. Talk in a happy voice - "OHH, what IS it??" Slowly get the treats and the dog closer to the street. You want him to associate cars with good things! He will soon think that the appearance of cars causes hot dogs to rain down.
This could take a long time, so you must be patient. Never EVER force, or drag your dog towards the cars. He depends on you to protect him. He must go at his own pace, and if you force him, he will lose trust in you and that will reinforce his fear. You found out that using "aggression" makes it worse!
I also suggest obedience school - excellent for bonding and for giving dogs confidence. My dog did get over all her fears, but it took a few months.