Quote Originally Posted by entre3D View Post
This all started sometime after installing aluminum Z arm upgrades. This was the 2nd of 2 printers I installed on, no issues on printer 1. I wonder if it's related. I'll try removing the threaded rod and re-installing. MB support says they've not heard of this.
The first thing I wondered, was if you had modified this in anyway. Imo I would think that is somehow what introduced the problem. When the build plate moves down on its own, can you tell if the rod itself is spinning, or does it appear that the threaded rod is stationary? If the rod is stationary than it must be the bearings or bushings. If the rod is spinning then it must either be the motor or the connection point between the motor and the rod.