Why doesn't my 3.5-5.6 lens open over F5?

Here's the deal, I've got a 16-85 VR , it's a 3.5-5.6, but recently is not opening up past F5. I've cleaned the contacts with eraser, to no avail. What else can I do? It does the same on two bodies, so it's not the camera.

Thanks in advance.