Im looking to reset my career when I get my Fanatec ClubSport in the coming months so i can play though the whole game with a wheel.
my question is is there anyway I can retain special cars like…for example my fallout f100 or my “team forza” cars
No. Why don’t you just restart the career races if you want to do them again?
A sense of progression is very much a driving motivator for me in games, its actually why I dont spend alot of time in my PC sims since there is very seldom a career with progression in them. Way more often then not they just have a do whatever the hell you want way about them and I get very meh about games like that.
Just do a new profile fella. No need to lose all your cars a progress. If its just a sense of progression your after then just do that
You could always create another gamer tag and do the ‘replay(s)’ using that one. It won’t have the special cars or any user specific DLC though, those will stay intact under your main gamertag.
This is what I’ll do because with the xbox one you can share gold with other accounts that are on that xbox. DLC packs will still be available for use though with the second account.
To answer your initial question…no. Gift cars you received from various events, Forza history (the cars you got based on your Forza Rewards Tier at the start) and/or being VIP will NOT stay in your garage, nor will credits, tokens (maybe?), and any cars purchased.
The Team Forza cars you will be able to buy again in the “Find a Car” menu, as they are considered DLC. Any DLC packs you purchased will stay purchased too, so those cars will be available to purchase as well. Additionally, any car you were able to buy via codes if you had the code (Pringles Edition MX-5, Dom’s Charger, etc.) should be available to purchase too, but don’t quote me on that. I’m not sure on whether or not the “one time free” rule for DLC cars will apply when you restart your game, but simply making a new Gamertag and profile will not give that bonus.
Edit: So summed up, the Fallout F-100 would be gone, the Team Forza cars you can buy again. One thing to note…if you are a VIP member, if you restart, you might not have the crown next to your name, and you may or may not be able to get future VIP gifts and race in VIP Rivals events. You can, however, still buy the VIP cars. Maybe you would have them, maybe you won’t. I don’t know, so I’d do a bit of looking around first (or wait for someone with a definite answer) before you do so, if you are a VIP member. If not, then disregard 
Disappointed to hear this I get why they removed car trading with how many exploits the FM series has had in regards to this, but would make my life so much easier.