i've read that you should do this gradually... Maybe monday you guys just take a little walk around the car... praise praise praise
then Tuesday you open the car door and sit on the seat with him and praise. or bring his favorite toy or treat... but staying very calm ... don't raise your voice even in excitement.. the car is not a big deal so try not to make a big deal out of it.... Wednesday maybe you guys sit in the car while it is running with the doors closed and radio on.... Thursday.. you pull out of the driveway and back up it a few times... Friday you are able to go around the block... now i'm not saying these days will go like this.. you might need to repeat day 2, 3 or 4 times before he is ok with it... and maybe you can have a key word... like... car ride.... and every time he gets in he knows he gets his favorite toy and a treat... but remember he needs to be somewhere safe in the car like a car seat or crate.. so that might be a WHOLE other stage.. getting him used to the car seat before it is even in the car... anyways.. this is just what i read in a magazine
take it slow... some dogs NEVER get there.. you might want to try something called Rescue Remedy.. you can get it in petsmart.. it's a natural calming oil you put on their tongue.. might work better. Good Luck