Saving Viewmodel data to the Database in ASP.NET MVC

I am new to ASP.net MVC and am using a viewmodel rather than viewbags to populate my dropdowns since I've seen most people recommend against them. I have a slick UI that does cascading dropdowns and autocompletes (not shown here) but I can't seem to get my data saved back to the database.

Models:

   public partial class Car
    {
        public int CarID { get; set; }
        public string CarName { get; set; }
        public int ModelID { get; set; }
        public int ManufacturerID { get; set; }
        public int CarColorID { get; set; }
        public Nullable<decimal> Price { get; set; }
        public string Description { get; set; }

        public virtual CarColor CarColor { get; set; }
        public virtual Manufacturer Manufacturer { get; set; }
        public virtual CarModel CarModel { get; set; }
    }
   public partial class CarColor
    {
        public CarColor()
        {
            this.Cars = new HashSet<Car>();
        }

        public int ColorID { get; set; }
        public string ColorName { get; set; }

        public virtual ICollection<Car> Cars { get; set; }
    }
   public partial class CarModel
    {
        public CarModel()
        {
            this.Cars = new HashSet<Car>();
        }

        public int CarModelID { get; set; }
        public int ManufacturerID { get; set; }
        public string CarModelName { get; set; }

        public virtual ICollection<Car> Cars { get; set; }
        public virtual Manufacturer Manufacturer { get; set; }
    }
   public partial class Manufacturer
    {
        public Manufacturer()
        {
            this.Cars = new HashSet<Car>();
            this.Manufacturer1 = new HashSet<Manufacturer>();
            this.CarModels = new HashSet<CarModel>();
        }

        public int ManufacturerID { get; set; }
        public string ManufacturerName { get; set; }
        public Nullable<int> ParentID { get; set; }