I replaced both filters in my old Dyson and it works like new again. What I don't understand is why the post motor filter isn't part of a guide on the Dyson site and that's why my Dyson didn't work. I didn't even know it was there and it took me 2 minutes to replace it. It wasn't until I wanted to buy a pre-filter that I saw this and bought the combo pack. Now everything is in order.