I recently repaired the hydraulic ram for my autopilot
and learned some lessons that might be good to share. My autopilot electronics
that I installed 10 years ago, but the hydraulics are Lecomble & Schmitt (France) probably installed in late 90's. I believe most hydraulic systems work the same way so, hopefully, this may help others with the same problem. Symptoms: The electronic components appeared to be working normally, but the rudders/helm were moving erratically. The 12V DC pump was running, but the helm
was not moving or moving with a jerky motion. The autopilot would alarm
since it could not correct to course.
The first step was to isolate whether the problem was with the hydraulic pump or with the hydraulic ram. A friend helped me diagnose this and the solution was to turn on the autopilot with the rudder
position indicator disconnected (small mechanical device attached to rudder
quadrant). This procedure activated the solenoid on the hydraulic pump to prevent hydraulic oil
from free flowing from one side of ram to another. Disconnecting the rudder position indicator allowed us to turn the helm
without the autopilot brain trying to correct back to course. In theory, this set up should have hydraulically locked the helm. With the helm "locked" we were able to slowly turn the helm even though it should have been locked by hydraulic fluid in the ram. We concluded that hydraulic fluid was leaking past the seals
in the piston of the hydraulic ram and the ram was the culprit.
I took the ram to a hydraulic repair specialty shop in Tampa and they replaced all the seals
(piston and seals on both ends) and leak checked the ram. I reinstalled the ram this week and bled both the hydraulic pump and the ram. The autopilot is working normally again.
The cost of repair was $125 which was a great deal compared to the cost of a new ram $2,600.
I also had an early symptom of this problem that I didn't recognize until now. When the temperature was cold (40's F) the AP wouldn't hold course and would alarm
. After it warmed up it would work normally. I believe the piston seals in the ram were leaking due to cold, but when they got warmer they expanded and worked normally. After a couple years the temperature threshold climbed until it was an "all temperature problem."