It should brake when you have some speed forward or backward. If speed is lower than some value (10cm/s I think) then it will start moving in direction of button press, otherwise it will brake. Or you mean something else?
EDIT: To be more clear. If tank is moving forward than back key is brake. If it’s moving backwards than forward key is brake. This is suppose to be more “typical” game controls.
I can make a separate binding for Steel Beasts version of controls. Which is much easier to implement as I don’t need to bother with measuring speed and deciding which way it’s moving and which button should brake it.