Your problem is not uncommon and if you check the troubleshooting section of the operators manual it gives you a list of things to try to correct the situation.
It would help some if you could post the settings you are using now. And how is your combine equipedIJ How far closed are the concavesIJ I dont have enough info to go on, but if I had to guess, which I should'nt, but I will, I'd start to think your concaves might be too far closed.
due you have a rubber flapper on your left side auger shaft under the roter this will help with even distrabution on your sieves if you need more info just e-mail me
Start at the source of the problem - the contact point. Should be at about bar n6 from left side. Unless your 1480 has been updated though the right side concave hangar plates are not adjustable. You can either slot the mounting holes or change to the 16 series plates and draw bolt.