It is definitely a scary thing to be going along and suddenly experience a bad case of front end wobble, shimmying or shaking whether you are in a car, motorcycle, bicycle or trike. It can be quite unnerving … downright scary. And it is even scarier when it happens at a high speed which seems to be when it happens the most. You can be going along and everything is fine … then suddenly you are like Elvis … all shook up.. My experience is that hitting a bump just right (maybe just WRONG) sets off the front end shimmy. About all one can do to end it is slow down. Of course, we would much prefer this doesn’t happen. So what is the cause of it? That is not something that can always be answered quickly and accurately as it can be the result of one of a few different things or a combination of them. It can be worn front end components such as tie rod ends. It can be poor inferior design. Some trikes are simply not made well and are well known for this problem. It can be toe in adjustment is off. I personally find that the most common cause is the headsets need to be reset as they loosen up. The type of headsets that Catrike uses is notorious for this. Catrike in their excellent engineering even redesigned the headset as the stock headset had a bad problem of shimmying as the manufacturer designed it. Catrike removed the upper bearing and replaced it with a Teflon bushing to help with this. BTW, Catrike owners may need to replace these at some point in time. You can get them from a Catrike dealer, from Catrike or other sources such as Utah Trikes. They can be bought individually or you can buy both for $25.
This Utah Trikes video covers resetting the headsets … starting at about six minutes into the video … and again at about 7 minutes 50 seconds into the video.
There is one thing that was not mentioned and seldom is. For the best results the rider should be sitting in the seat in the riding position so that the rider’s weight is loaded onto the headsets. This works best to have someone else do the mechanical work unless someone else can take the rider’s place who weighs the same. With proper headset adjustment it should help to eliminate front end shimmy. I wish you well in resolving this issue. It has worked for me. Do your best to be safe so that you can …
KEEP ON TRIKIN’
A FREE GIFT awaits you!
Tadpole Rider 
I had a front end shimmy on my ICE trike & learned where the steering attaches to the trike frame there is a set screw with word “damper.” Tighten it and the shimmy is gone.