Posted 25 July 2015 - 01:27 PM
Until you posted in answer to Rick's question(s), I did not know you had a 12 inch on that LX 90 mount. In fact, I had not noticed that they had started selling the 12 inch in an LX 90 format. Your jerk problem may be associated with the scope really being at the very upper limit of what the mount can take, if not over that limit a little.
With this knowledge, I suggest that you not manually run the mount at higher speeds. I do not know that you can break anything inside the mount, but I do think there is a greater probability of something going wrong with the greater mass of the scope.
Sky Hunters' Haven Observatory,
Broken Arrow, Oklahoma