Replacing hydronic trim tab actuators

[Roger K Sterling]

One of my trim tabs stopped moving. I can here the motor trying to move it. This is a hydrolic system. Im going to replace the actuator. Should I expect the fluid drain when I remove the actuator?

 

[hughespat57]

If they are hydraulic there is a tank and pump with two solenoid valves.

Did you check the fluid level?
Any oil in the bilge?
More often its the solenoid valves or leaks

the ram is very simple oil pressure to extend, spring pushes it back in for retraction.

They either work or leak oil out the end not much else in them to go wrong

 

[Bill Curtis]

One of my trim tabs stopped moving. I can here the motor trying to move it. This is a hydrolic system. Im going to replace the actuator. Should I expect the fluid drain when I remove the actuator?

As far as the oil is concerned, pulling the actuator will not dump the oil in the tank. Be sure to hit the tab up button for a few seconds after the tab is full retracted, relieving all the pressure, if any. Position a rag beneath the connection, as it will dribble some small amounts of oil out.

As stated above, it is not common for the actuator to fail like you describe, and it is usually the solenoid or a little terd of gunk blocking the ports in the valve under the solenoid. You could swap the solenoids from side to side and see if the problem moves to the other tab. Or swap the hydraulic lines at the pump to see if the problem moves. I would swap the lines, as that it is a fast test and distinguish between a pump assy or actuator problem.

 

[Roger K Sterling]

I removed the hydraulic actuator and the fluid started steaming out so I quickly reconnected it and now it's working fine, full ranfe of motion and moves quickly. However the actuator that was working fine is now working poorly. Should I remove it to let it bleed and see if that fixes it?

 

[Bill Curtis]

Normally, just running up and down, full stroke, three times will purge them. That is of course, if there isn't some funky hydraulic line routing causing an "air trap".

Still think there is something going on with the HPU (Hydraulic Pump Unit). I would pop out both solenoids, pull the valve out from under them and check that they are clear and clean.

Ton of Bennett videos on Youtube and the Bennett site addressing things like this.

My tabs work great now, but when I bought this boat, tabs were all messed up
1. It had 2 different 4 ring actuators on it with different strokes (yes, Bennett did make different OEM versions of different strokes, using spacers under the piston).
2. HPU did same as yours, pumping speed was different between tabs.
3. One button was sticky.

I did the following:
1. Modified the actuators so they had the same stroke
2. Since the HPU was 27 years old and weeping oil from the seams, I replaced the whole unit with brand new.
3. Replaced the twin button setup with the new unitized LED indicator / controller. A word of warning that Bennett makes no mention of this anywhere.
A. The sensors that replace the top hinge require the use of a spacer at the top of the piston to prevent sensor from bottoming out in up position. This will change your full up tab position LOWER when reinstalled in the original upper hinge position (holes in transom). The new upper hinges caused the tabs trailing edge to park about 3/8" Below CL of hull. The 12" tab trailing edge should park 1/2" above center line of hull bottom.
B. I corrected by re-drilling the lower hinge mounting holes in the S/S tab rearward about 3/4". This corrected the upper park position, but slightly reduced the lower stop position and slowed movement slightly. This isn't a problem, in my case, as I believe the boat is over tabbed to begin with.

 

[Roger K Sterling]

Appreciate your reply. I have one more thing I'm going to try.

 

[Roger K Sterling]

Ok it was the switch on the dashboard. It all working now.