It's time to ask for help.. this might drive me insane.

Been working on my Z axis.
The ballnut bracket didn't really fit under the dropplate. I could squeeze it in but it jammed in the ends so I took a file and sandpaper and reduced it about 0.5mm in hight. Now it slides perfect under the dropplate. When I then tighten the bolts that hold it to the dropplate the ballscrew turning becomes stiff and "juddery" in one direction. Smooth but with a little resistance in the other direction. Something must be crooked?
The ballnut is really smooth without load and I can pull it either direction to make the screw turn.. what should I check and do??