My Cokin z pro holder causes vignetting at 18 mm on my Nikon 18-35 mm and the problem is accentuated if I have to screw it on top of a polarizer. Anyone else had this problem or have any solutions? I am using the Cokin provided filter holder and the lens thread is 77mm.
There is a limit to the amount of length you can add to the lens barrel before it starts blocking the light that enters the lens. The determining factors are the angle of view and how far back the front element is from the filter threads. The current version of your lens has a front element that's more recessed than its predecessor, so that factor gives you less room to work even though the widest focal lengths are the same.
I think the Z series holder is already good for wide-angle use (the P series has a different holder for that purpose), so the best you can do is get rid of your polarizer or switch to a slim one if you're not using one already.