Can anyone help me my wheel collider code doesn't work

I have these coded for wheel coliders but they dont move when the code is used the vehicle just kinda vibrates but if i make the brake value 10 and the acelleration value 100 the vehicle will reverse only. and then a couple seconds later it just starts flipping wildly is ther anything wrong with this code:

var speedDefault : float = 10; var brakeDefault : float = 100; function FixedUpdate () { if ( Input.GetAxis("Shoulder Axis") > 0.1){ if (collider.motorTorque < 0 ){ collider.brakeTorque = brakeDefault * Input.GetAxis("Shoulder Axis"); }else{ collider.motorTorque = speedDefault * Input.GetAxis("Shoulder Axis"); } }

 if ( Input.GetAxis("Shoulder Axis") < -0.1){
     if (collider.motorTorque > 0 ){
         collider.brakeTorque = brakeDefault * Input.GetAxis("Shoulder Axis");
     }else{
         collider.motorTorque = speedDefault * Input.GetAxis("Shoulder Axis");
     }
 }

}

or could it be something else causing this to happen really strange like thanks to anyone who can help.