My first impulse would be to check the bypass valve. Our hydraulic autopilot
has a ram attached to the steering
quadrant. When in autopilot
mode, moving the quadrant manually forces the ram to move.
On our system, if the bypass valve is in the 'autopilot' position, the steering quadrant will only move <1/2". With the bypass valve in the "manual" position, fluid flows freely and the ram moves back and forth with the steering quadrant.
It may be that your bypass valve is not opening all the way so that you have to force the hydraulic fluid through a very small orifice.
Other troubleshooting checks on my list would be the condition of the ram - unbolt it and see if it moves freely and steering cables
- maybe the ram is strong enough to move the quadrant against a lot of friction in the cables
Please post whatever you finally figure out. Since it sounds like we have similar systems, I'd like to learn from your experience.