Car simulation, motor torque and brake torque combine problem

I am creating a custom wheel collider in Unity. Every thing is fine now (suspension, collision, friction) except one problem that i cant get my head over for last 3 weeks. So now i have a car (one wheel only), it stand on top of a hill, then i apply a brake torque enough to make it stand still, after that i apply a motor torque that less than max brake torque, my question is how the car behave?. In my opinion, that if sum of motor torque (roll down hill direction) and gravity torque(friction force * radius) greater than the max brake torque will cause the car to roll down hill, and it remain stand still if motor torque (roll up hill direction). I really need help!