Translating in world space only on y axis?

I'm translating a car to simulate speed and it works fine except when the car goes uphill and gets in the air, it goes crazy and starts flying everywhere, I tried lowering the translation power while in mid air but it seems very unrealistic and not very fun. Basically I want the car to be able to jump off ramps and hills without flying everywhere. If I change translation to world space, rotating the car loses it's effect, so i was wondering if there is a way to turn the y translation non affectable by the car's y rotation during mid air. I thought about it a lot and searched around but I couldn't find a viable solution.