How to add dirt on a direction of the object I have modeled a car and now im trying to texturize it. I would like to make the materials proceduraly, so I have not unwrapped the model (if its necesary I will, but I dont want to bake the textures).

My problem its that I would like to add dirt at the bottom and front of the vehicle, and I dont know if there is a way to do that, for example, in Substance Painter you can set a direction and it will make a mask with that, but I dont know any way to do that.

I have seen this video: https://www.youtube.com/watch?v=ZmrCoGj9m2Y
but it doesnt seem to work to me 

Im using blender 2.8. Thx

The model:
If you need to give your dirt a direction, other than the object-Z illustrated in Andrew Price's tutorial, you can 'shine' the dirt onto the surface from any point in the object's space.

If you take the normalized Dot Product of the Normal at the shading point with a vector (which you can visualize as a point in the object's local space), then the resulting 0-1 value looks much the same as if the object was illuminated from that point. You could also put the Normal Texture coordinate through a 'Normal'node, but that doesn't take numerical entries, and isn't quite as controllable.

... You can use the value as the factor in a mix between your clean and dirt shaders.

You also have the option of using a Geometry node &gt; 'Pointiness' attribute as a component in the mask, to add dirt in crevices.