Last year I added "add on" hydraulic steering on my old Formula. I connected up the hydraulics & was getting the bubbles out by turning the steering wheel side to side. I started the engine and turned the wheel & "WHAM" it spun out of my hands to full stop!!
Well, I found my lines were reversed at the Mercruiser cylinder, so I fixed that.....but the steering was stiff as everyone has said it would be. used it all summer. Last fall, I pulled the engine to refinish the engine bay and discovered the steering cable rod that attaches to the Bravo arm was double bent about 1" out of line and the tube it runs thru was broken completely loose. I cannot figure out how this stainless steel rod could get bent. This is the rod at the end of the steering cable. The boat never (to the best of my knowledge) has hit anything. No marks, etc.

Has anyone ever seen this????
I, needless to say have now installed full hydraulic helm set up.

Did you ever figure out what caused the wheel to jerk that one time?

I would say it got bent when the stearing went full lock. Your lucky you didn't tear the rams out of the transom or break the wing plate.

I thought so also about the lock to lock thing. I guess it was hydraulic surge that caused it. Man o man, if my fingers had been in the wheel, they would be calling me "stumpy" now! What is really strange is how that bent rod (it was a pretty sharp bend) could move in the cable housing! This was radical!

IMCO has a warning in their brochure against this. If it's as violent as you report, just be glad your thumbs weren't in the wheel.