ember-cli - can't createRecord with belongsTo relationship

When I'm trying to create a record, only one property is created.. I'm using belongsTo relationships. I have a car model:

//car.js model
import DS from 'ember-data';

export default DS.Model.extend({
  manif: DS.attr('string'),
  type: DS.belongsTo('type')
});

And I can send the manif: 'something', but the type will always be null. I tested it, ex. type: 123, but still in my database its null.

Thanks.