Motor Moving Problems

[WlsRostock301]

Hi,
I' sorry i come from Germany and i dont know if my english is so good but i'll try.
We just bought a Geetech Rostock 301 and after solving most of the Problems we now have one we can't solve.
When the Hotend is moving the motor on z-axis randomly clatters(I don't know if its this in English) some millimeters.
We already tried to adjoust the tension of the belt and we gave the motor more Power with the Potentiometer.
It just helped a bit. Maybe someone has the same Problem and can help us!
Thanks in advance!

[Gingko]

1, Maybe the driver(A4988) of Z-axis is broken, swap the driver with the X-axis driver for inspection.
2, Compare the wire of Z motor with the wire of X and Y motor, check the colors, and see whether the order of the colors is the same.

[WlsRostock301]

Thats not the problem. We build in other motors but they were worse than the others. So we switched to the original ones and now the haven't got enough force to press the endstops. They are able to move the hotend.

[_kaktus_]

Have you checked whether the mechanism can be easily and gently sieved on the linear rollers?
If you feel resistance while moving, it will not work well.