Vehicle chassis physics

Not sure if this is the right board to post in, first post. I'm trying to create a realistic vehicle in unity and I've managed to get it moving around the way I want, the problem I have is with the chassis. I'm trying to find a way to put an axle in and have it behave like an axle. pictures underneath to try and better explain:




Here's a picture of what I'm trying to achieve, but when i run the game the physics of the bod mesh are applied to the axle too, and it drops/wobbles with the body.

Any help really appreciated.
Thanks.