Backlash on Z-axis after service

Hi all,

I have my SC2 840 for a couple of years. I moved it, so I figuered why not clean it very well and re-align.
Turned out this was not my best idea. Most of the problems I solved. Trail and error and some help of youtube.
Unfortunately I now have a little backlash on my Z-Axis. I don't know where is came from, and don't now how to get rid of it.
Can anyone help me by sharing his/her thoughts on this?
In words, if I puth up on the bottom of my Z-axis it moves a litle upwards. I don't have the tools to measure it. But if I'm able to feel it, I gues it is enough to worry about. It is like there is a little play in the ball bearing nut. To my knowledge it wasn't there before I serviced my machine.

Please help, what can I adjust to remove this tolerance.
Thank you!

Mathieu