Hello all. I own a 1997 Grand Banks 49 CL. About 2 years ago, we replaced the original Raymarine autopilot with a Garmin Reactor retrofit unit. We did not replace the Raymarine autopilot pump. In Spring 2021, we found the AP pump and the steering cylinder were leaking (this may have predated the AP upgrade). We installed a new Octopus OCTAFG1612 AP gear pump and a new Teleflex HC5379 steering cylinder. The autopilot worked great for about 2 months of weekend use at which point it started squealing and leaking fluid. Octopus replaced the AP pump under warranty. After about another 2 months of flawless performance, the replacement AP pump also started squealing. After consulting with Octopus and with Garmin, we replaced the gear pump with an Octopus 2012 reversing piston pump.
The AP has never functioned properly with the piston pump. The AP will hold a course for about 30 seconds and then drifts at an increasing rate either to port or starboard. If we nudge the wheel, the AP will return to the original course, but immediately begins to drift off course again. The Garmin AP electronics have never thrown an error code. Replacing the Garmin ECU and CCU did not solve the problem. We suspected a blockage in at least one of the upper or lower station Capilano helm pumps and sent both to Seastar for rebuilding. Seastar found and repaired a blocked valve in the upper station pump. Both helm pumps were reinstalled.
The problem continued, so we installed pressure gauges on the port and starboard connections of the AP pump. Those gauges show about 200 psi in both legs as soon as the AP is engaged. This suggests that there is still a blockage somewhere in the system, but I have no idea where. When steering manually, the active leg shows about 200 psi, but the inactive leg shows atmospheric pressure.
Sorry for the lengthy history. Does anyone have a suggestion about possible causes or solutions?