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How to Maintain a Boat Trailer

a vintage Volvo Penta Sterndrive on a trailer boat

Boat trailer maintenance tips, tricks and techniques you should know

The most important boat trailer maintenance task is to lubricate the wheel bearings. Wheel bearings heat up on the road from home. Then at the launch ramp unceremoniously plunge into cold water. The rapid temperature change cools the air inside the hub producing a vacuum, which in turn sucks water into the bearings. The water contaminates the grease. Over time the bearings corrode and eventually seize. A solution to this malady is to install bearing protectors, popularly known as Bearing Buddies, which maintain positive pressure inside the hub keeping water out.

trailer axle components

Photo courtesty Tie Down Engineering

To work on the trailer requires a jack, jack stands, a large flat-head screwdriver, a ball pein hammer, a pair of needle-nose pliers, clean rags, a small pan, a quart of kerosene a spray can of brake cleaner and a block of wood. Loosen the lug nuts on the wheels. Block the tire on the opposite side of the trailer to be worked on. Jack-up the trailer and support that side with jack stands. Spin the wheel and listen. Best case scenario is if the wheel spins freely and the wheel bearings run quietly. But if you hear noise, howling or grinding, or the wheel does not spin freely, then the wheel bearing or spindle is damaged and requires replacement. If all is well remove the tire and wheel.

Trailer manufacturers recommend repacking wheel bearings annually with normal use, or at least every 20,000 miles

Pry off the dust cap loose with a large screwdriver. Straighten the ends of the cotter pin then pull it out with a pair of dykes. Unscrew and remove the axle-spindle's castle nut. Slide the hub off the spindle. Deftly reach inside the hub and remove both bearing cages. Soak them in solvent or kerosene to remove the dirty grease. Do not make the mistake of drying the bearings with compressed air because the air pressure will spin the rollers wildly and burn them out. Also, clean the surfaces of the bearing races located inside the hub.

Trailer Spindle and Hub-component

Trailer Spindle and Hub-components

Remove the seal by tapping along the rim of the bearing with a block of wood and a hammer. It's commonplace for the seal to be rusted to the back of the hub. No problem. Spray a dab of WD-40, or equivalent. If the seal is damaged, replace it.

Clean all of the old grease from the bearings, races and seal. Once clean, inspect the components for wear and replace if needed. Once bearings and parts are clean, spray with brake cleaner. Similarly, spray the spindle and the inside of the hub then wipe with a clean rag removing all of the old grease.

Lisle wheel bearing packing tool

The Lisle bearing packer pictured above costs less then $10.

Pack the bearings with marine grade grease. This can be done by hand, but a better method is to employ a packing tool. Even name brand ones cost almost nothing and are worth it for the better job they do more-completely filling the bearing with grease. To use, place the bearing inside the plastic cones, tighten, then inject grease through the zerk fitting at the end of the threaded shaft. Pumping the grease gun expels old grease and injects fresh grease. To pack a wheel bearing with grease by hand, work from the wide side of the bearing, manipulating grease into the bearing. Push grease into the roller until the cage and rollers are filled, then coat the inside of the hub with grease.

wheel bearing grease seals

Using a block of wood tap the seal back into its recess on rear of the hub. Assemble the hub and bearings back on the spindle. Thread the castle nut back onto the spindle, turning clockwise. Spin the hub a few times as you tighten to make sure the bearings are seated properly. Tighten the nut firmly. Now back the nut off about an eighth of a turn until the hole in the spindle aligns with a gap in the castle nut. Restated for clarity: Adjust the axle nut, not so the tightly bearings bind, but tight enough to eliminate side-to-side play.

Push in a new cotter pin (available at hardware and auto parts stores) and bend the ends of the pin to keep it from working its way out. Tap the dust cap back into place. Coat the hub lug threads with anti-seize compound. Reinstall the wheels and tighten their lug nuts.

Check the winch buy unfurling the cable or strap. Patiently check the entire length for chafe, meat hooks (broken wire strands) or corroded swage fittings. When in doubt replace.

Walk around the frame checking every square inch me for buckling, cracks, or rust. Pay special attention to welds and attachment points for fenders, bunks and rollers and the winch. Grind rust down to bare metal with a brass wire brush then paint with a corrosion-inhibiting primer. Primer is best applied in a thin coat. Let it dry completely between coats in order for its volatile chemicals to out-gas. Rebuild the finish with several coats of paint. Apply in a smooth swipe, don't swish the can back and forth or the excess paint will accumulate and sag. Take your time for a professional looking finish.

Check rollers and bunks with the boat in the water. On bunks, replace the carpet if worn. Lubricate bunk pivot points with light oil. Check the pivots for corrosion. Make sure the rollers spin freely and their axles are straight, not bent. When replacing rollers know that yellow polyurethane rollers last longer than black rubber and do not leave unsightly marks on your hull.

Check axle U-bolts and nuts. Squirt a a dribble of WD-40, or equivalent corrosion inhibitor, onto the threads. Give the stuff a minute to work then back off the nuts. Lubricate the threads, then re-tighten. Make sure the trailer coupler locking lever is in good condition, not bent or cracked and that the coupler safety pin is present and in good condition. Replace a badly rusted coupler, cheap insurance against a disconnected trailer running wildly down the highway. Wire brush any rust on the coupler.

Cracks and breaks in the frame should be welded as soon as possible before they worsen. Examine leaf springs for broken leaves, but do not attempt to repair one yourself. Instead, seek professional counsel. Inspect the shackle bushing by removing the shackle bushing plate. This is the assembly that bolts the spring to the frame. The rubber bushing that surrounds each bolt should tightly grasp its bolt without slop. Worn bushings can be pulled out with a pair of pliers and a new one tapped back into place with a rawhide mallet.

Inflate the tires to full pressure. Sink a penny into the tread. The copper/zinc coin should sink into the groove as far as Lincoln's beard. Any less and the tread is excessively worn. Inspect the sidewall for cuts and breaks. Side wear is the most common kind of wear and indicates a bent axle. Tube axles can be realigned

Make sure all of the bunks or rollers are adjusted to support the weight of the boat. If any are out of line, back the trailer into the water just enough to make the hull buoyant. Adjust the height. In colder climates with bone-chilling water temperatures you may prefer waiting until spring or summer.

With the connector plugged into the tow vehicle, check all of the running lights for dead bulbs. Replace burned out bulbs as well as cracked or broken lenses. A dab of Vaseline or grease smeared around the periphery of the lens gaskets helps keep out water.

Preventive Maintenance

Hitch up the trailer to its tow vehicle and drive around the block every couple of months to keep the brakes from locking up.

Thoroughly hose down a trailer after each use. Know that saltwater, or freshwater high in acidity, or low in alkalinity, require a galvanized or aluminum frame trailer. A freshwater rinse of the trailer, including the brakes, extends their lifespan. Don't neglect the wash coupler and winch! For painted trailers, car wax protects the finish. Dealers stock touch-up paint for repairing minor damage.

On bunk supports, make sure the carpet is free of sand and other debris. On roller trailers, keep the rollers clean.

If the current winch is undersized, or in bad shape, consider replacing it. A winch is designed to launch and retrieve your boat, neither but it is not intended to hold the boat on the trailer while happily cruising down the Interstate. Trailer winches are not tie-downs. Boats require a dedicated tie-down line attached from the boweye to the trailer tongue, or winch stand.

Know that one way to increase wheel bearing life is to replace a trailer's wheels with larger diameter tires, which, in turn, reduces bearing rpm. Many small trailers ride on tiny, 480 x 8 wheels. If the fenders allow an increase in diameter, consider going up a size, replacing 480 x 8 wheels with 570 x 8 wheels.

Lisle wheel bearing packing tool

CE Smith Spare Hub Kit.

Consider keeping a spare hub kit tucked away in the tow vehicle in event the one on the trailer fails. All the parts store inside a rigid, carry case. Hubs come fully assembled with pregreased bearings and the kit includes a spare dust cap, cotter pin and lug nuts.