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Author Topic:   Trim Tab Repair
Smallfrye posted 05-21-2003 09:46 AM ET (US)   Profile for Smallfrye   Send Email to Smallfrye  
My [used] boat came with non functional Bennett trim tabs. Since I have no experience with these items I hope you all can help me through the learning curve.
The fuses are OK, the switches function but there is no movement of the tabs or in the pump/ motor area. Are there [known problems] I should be looking for?
Are the cylinders on the tabs simple hydraulic cylinders or is there more in there ?
Are all the key components in the pump/motor assembly and what normally breaks first ?
Thanks for any assistance.
Tabman posted 05-21-2003 11:57 AM ET (US)     Profile for Tabman  Send Email to Tabman     

Below is troubleshooting. Take a look at the connections at the switch and the black ground wire. How old is the system? Let me know and I will be delighted to help you get the system running.

Tom McGow
Bennett Marine

Fluid: Automatic Transmission Fluid (ATF) any type. Hydraulic Power Unit is self bleeding, running the Trim Tabs up and down 3-4 times will purge air from the system.

Fuse: 12 volt system use 20 amp in-line fuse on positive. (24v & 32v use proportionately smaller)

Red= Port Valve
Green= Starboard Valve
Blue=Motor Forward (pump pressure)
Yellow= Motor Reverse (pump retract)
Black on HPU=Ground
Orange on Helm=Control Positive


1.If one side is not operating reverse hydraulic lines on the front of the Hydraulic Power Unit to determine if the malfunction is in HPU or actuator / hydraulic lines. If after reversing the lines symptom shifts to the other side the malfunction may exist in HPU. If the symptom remains on the same side, malfunction may exist with the actuator / hydraulic lines

2. Is the unit receiving a solid 12 volts? Low voltage will some times cause the solenoids to not open preventing the tabs from moving even though the pump motor is running.

3. Conduct the following test:

Remove the wires from the helm control and touch together as follows:

Orange (+), blue, red= Port trim tab down
Orange (+), blue, green=Starboard trim tab down
Orange (+), blue, red, green= Both trim tabs down
Orange (+), yellow, red= Port trim tab up
Orange (+), yellow, green=Starboard trim tab up
Orange (+), yellow, red, green= Both trim tabs up

If the trim tabs function correctly for each wire grouping then the switch is at fault. Also note that any loose or missing screws on the back of the switch (whether a wire is connected there or not) can cause the pump to malfunction.

This test may also be done right at the pump by substituting a "hot lead" for orange. There is usually a connector to the wire harness within a foot or so of the pump. You want to check this connection for corrosion. You may wish to cut the connector off on the pump side and try the test on bare wires.

4. If you suspect corrosion on the wire connector near the pump, cut it out, test as above and reconnect using butt splices.

5. If you conclude the problem is in the pump, contact me. Bennett Trim Tab Systems carry a five year warranty. We also offer a trade in program for units out of warranty. Contact us for further details after you troubleshoot the system.

6. Check to see if there is a relay in line on the wiring harness near the hydraulic power unit. If there is it is an Interrupter Relay (IR1000). It prevents the system fuse from blowing if you try to actuate one trim tab up and the other down at the same time. After you test as outlined above, try removing the relay from the wiring harness and retest the unit. If it works the IR1000 will need to be replaced

Montauk posted 05-21-2003 12:35 PM ET (US)     Profile for Montauk  Send Email to Montauk     
I am truly impressed that Tabman monitors this site along with all the others he replies on. Keep up the great work Tabman!
Smallfrye posted 05-22-2003 09:32 AM ET (US)     Profile for Smallfrye  Send Email to Smallfrye     
Thanks Tabman, I will run through these checks over the weekend and let you know what happens.
mycig21 posted 06-21-2008 08:02 PM ET (US)     Profile for mycig21  Send Email to mycig21     
I just [five years after this discussion was begun] removed trim tabs from boat and reinstalled, but did not touch pump. I did remove the lines but [believe] the Bennett [hydraulic systems is] self bleeding. After reinstalling the tabs, they are not operating. Prior to removal they were fine. Now, I hit the switches, the pump runs, but tabs do not move. Any ideas? I find it funny they were fine just a few minutes ago. A would appreciate any help I can get.
jimh posted 06-22-2008 08:26 PM ET (US)     Profile for jimh  Send Email to jimh     
Begin by reading the trouble-shooting procedure given above. Follow all the steps. It should help you locate the problem.
seabob4 posted 06-22-2008 08:47 PM ET (US)     Profile for seabob4  Send Email to seabob4     
One simple thing to remember. If you disconnected the hoses from the actuators, or if from the pump, re-caulked, and fed the hoses back through the holes in your hull, caulk may have plugged up the hoses. Been there, done that...

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