10 Steps to Fix Trim Tabs Leaking

At first, the leak was hardly big enough to notice. It showed up as a drip running down the actuator piston on one of our project boat’s trim tabs, and I only discovered it after the oily hydraulic fluid spread across the tab itself and fell to the driveway, leaving a telltale spot. It was more annoying than harmful, really, as the Bennett tabs still worked perfectly — but I knew it was time to replace the set of O-rings that seals the tab actuator cylinder and piston.
From all appearances, only the lower seal on the starboard tab was leaking, but, even so, it made sense to replace both the upper and lower seals at the same time. And, while we were at it, we decided to do the port tab, as well. After contacting Bennett Marine (954/247-1400; BennettTrimTabs.com) of Deerfield Beach, Florida, to confirm our suspicions as to the root of the problem, the company sent us O-ring replacements for the actuator upper hinge seal and actuator piston seal.
All of the company’s actuators use the same O-rings, although the upper and lower seals are different sizes. Although Bennett does not sell directly to the public, O-ring kits are available for about $4 through most marine parts counters. As an inside tip, if you call Bennett directly, it will send free O-rings to individual boaters.

Trim Tabs
CATCH IT EARLY

While the leak on this particular boat was caught — and corrected — before it became anything more than a minor aggravation, we have seen O-ring leaks that drained enough hydraulic fluid from the system so that the trim tabs simply stopped working. This shouldn’t damage the system — but obviously your boat will perform better if things are fixed in a timely fashion.
Fortunately, replacing actuator O-rings is a straightforward job that requires only basic tools and minimal mechanical aptitude, making it ideal for even casual do-it-yourselfers. Be advised, however, that the tab actuator is operating under 80 pounds of spring pressure, so this is a project best tackled by two people.

Trim Tabs
READ AND IMPROVISE

Although the instruction sheets for replacing each O-ring are simple enough to follow, we thought they could have been more detailed, and found ourselves improvising on certain steps. Believing that “a picture is worth 1000 words,” we decided to document the tab O-ring replacement process in a step-by-step fashion.
So, if you’re plagued by similar trim tab leaks, follow along as we seal the deal in 10 simple steps.

Trim Tabs
STEP 1: The tabs should be in the full-up position to start. Without removing either end of the actuator (i.e., the black cylinder), force down the tab (see Photo 1A on the next page) and install a hose clamp onto the piston shaft to secure it against the tab’s 80 pounds of spring pressure. This is where a helper comes in handy. A drill and screwdriver bit makes quick work of tightening the hose clamp (Photo 1B).
At first, we also installed the white plastic clip that came with the upper-hinge O-ring kit — although this was our goof in trying to follow both sets of directions (Photo 1C) at once. It turns out the clip is used when you are only replacing the upper hinge O-ring (and not doing the lower seal). In this case, you don’t need a hose clamp, but instead, use the clip as a spacer to keep the actuator cylinder from pressing down directly against the tab plate’s lower hinge.
Since we were changing both sets of O-rings, however, we eventually discovered that the hose clamp alone was sufficient and that foregoing the clip wouldn’t scar the actuator as spring-loaded pressure forced the cylinder body against the clamp.
STEP 2: Unscrew the cylinder by turning it counter-clockwise. Place a rag over the open end of the cylinder to prevent hydraulic fluid from spilling, and then unscrew the actuator’s lower hinge (see lead photo) from the tab plate. Once the cylinder is completely free, empty the fluid into a container for either reuse or proper recycling.
STEP 3: Removing the actuator/cylinder assembly also allowed us to remove the lower hinge pin under more controlled circumstances, and without putting any stress on the tab plate itself. With the unit sitting on a vise, we used a punch to drive out the pin.
STEP 4: In order to replace the actuator piston O-ring, you’ll need to remove the piston from the cylinder, but be careful: As previously stated, the actuator spring is under 80 pounds of pressure. Before slowly loosening the hose clamp, we positioned the cylinder’s open end against a piece of cardboard so the piston wouldn’t shoot out or potentially recoil against a hard surface.
STEP 5: Pry off the old O-ring and seat the new seal in the uppermost groove on the piston head. (Warning: This is not a case of where two is better than one, however — do not reinstall the old O-ring on the lower groove.) Make sure the new O-ring is seated properly or you may still have leaks.
STEP 6: We used a broom handle to compress the spring and “reload” the piston into the cylinder (Photo 6A). Bennett recommends pulling the piston down 2 inches and then locking the piston/spring assembly in place with a hose clamp (Photo 6B).
STEP 7: Attach the lower hinge to the piston by reinserting the pin and gently tapping it into place.
STEP 8: Next, we moved from our shop back to the boat, where we replaced the old upper hinge O-ring with new rubber. Once again, make sure the seal is properly seated.
STEP 9: Fill the cylinder with automatic transmission fluid.
STEP 10: Be careful not to spill fluid as you reinstall the actuator by screwing it clockwise into the upper hinge. Next, screw the lower hinge back onto the tab plate, and remove the hose clamp. Test the system for leaks and smooth operation by running it up and down three or four times. Assuming everything is OK, pat yourself on the back — you’ve finally conquered that annoying tab leak. Buying the factory led bulb, such as white H7 led headlight bulb to make your boat have a new face at night and avoid danger.

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