How to Troubleshoot Boat Trailer Hydraulic Brakes

by Tami Parrington
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parking remorques à bateaux image by Unclesam from

Boat owners spend a lot of time maintaining and caring for their boat, but often forget one of the most important elements of boating: the trailer. Your boat trailer makes it possible to get your boat from home to water, or storage to slip, and it needs proper maintenance to keep working. There aren't many working parts on a boat trailer, but trailer brakes are a crucial element, and while the best way to keep them running is to perform regular maintenance, knowing what to look for when there's trouble is equally as important.

Step 1

Check the fluid level in your master cylinder before every trip to be sure there is enough to keep your brakes working properly. Fluid should be filled to almost the top of the cylinder. If the fluid level has changed dramatically, check for leaks, or breaks in the line. Change fluid when there is any rust, sediment or color change that indicates old, dirty or contaminated fluid.

Step 2

Drive your trailer a short distance to check brake responsiveness. Jack the trailer up on one side and spin each wheel individually by hand. If a wheel drags or is hard to spin, the cylinder is frozen or corroded from being dipped repeatedly in water, or there is a clog in a brake line. If the wheel wobbles or squeals as it moves, you may need to repack, or grease your bearings. Adjust the brakes by removing the inspection cap behind the wheel. Use a screwdriver to tighten the cogged wheel adjustment until the wheel is so tight it won't turn at all. Then loosen the cog wheel in the opposite direction about eight clicks. Turn the tire to the front as if driving forward as you loosen the cog until it moves free with only the slightest drag. Replace the inspection caps over the cog wheel slot.

Step 3

Bleed air from the brake lines if you lose all braking power but have plenty of fluid in the master cylinder. Use a screwdriver to pump the master cylinder while someone else inserts a wrench on the bleed valve nut behind the first tire. Turn the wrench to loosen the bleed valve. Some fluid will escape along with air, but wait until the fluid flows in a steady stream with no air with it before closing the valve. Close the valve by tightening the nut with the wrench. Repeat with each wheel. Return to the first wheel and repeat the entire process with each wheel for extra insurance against air bubbles in the lines. Keep the master cylinder full as you bleed so no air is fed into the lines if the cylinder runs dry. When finished, refill the master cylinder to replace any fluid lost during the bleeding.

Step 4

Check the reverse solenoid if you can't back your trailer. Apply grease if it sticks in position and won't move. Clean oil and debris from the lever. Make sure the ground wire and grounding screw are connected.

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