About a year ago I replaced the standard Z axis by the k8204 upgrade. This made my Z axis smoother so back then I was satisfied. Now that I’ve upgraded a lot of other parts, the curve on the trapezoidal spindle started to be big enough to make a difference in quality. (the k8204 spindle was bend from the moment it arrived). A few weeks ago I ordered a TR8 X 8mm spindle and nut. This one is perfectly straight and has no wobble. The problem is that my printer seems to miss steps on the Z axis now. It’s a brass nut I ordered with it. Could it be that the pitch is too high and that’s the reason the Z axis is missing steps?
Hy,
there are various sizes of pitch with TR8, if yours is 8, you can see in the Reprap calculator the optimal Z layer height, have a look in following link in the section : Optimal layer height for your Z axis
I’ve tried pitch 1, the screw is too smal and make noise and get blocked.
I change with pitch 2, the results are good.
With pitch 8, the Z arm can go down by itself with the height 
then to avoid this problem, in configuration.h in marlin you must change #define DISABLE_Z true value to false.