[DG] [DG11] CR hydraulic drive versus Type 3 linear hydraulic

[shparrot]

I have a 57', 20,000 kg, sailboat with a semi balanced rudder weighing 54 kg. After stiffening the rudder post, redoing the ram mounts, connecting the rudder transducers directly to the tiller arms and updating software, both my type 3 linear drives, (dual ACU 400s with EVO), occasionally go into rapid oscillation. The pedestal / wheel movement becomes quite violent and I need to grab onto the wheel to settle the system. I can usually set damping to 7 or 8 in calm conditions and must raise it to 9 downwind or when seas are over 2.5 meters. This was an upgrade to an older 400 system which worked extremely well so I'm not sure what is going on. There was a second system, CR pump with balanced ram. (Guess I should have kept it.)
Would converting one of the ACU 400s with a type 3 drive to a ACU 300 with a CR2 pump solve the hunting issue. I wonder if relays respond more quickly than a pump stopping, starting and changing direction. Somehow, I need to reduce the system inertia.
Thanks
steve