Why salt water destroys trailer bearings
A hub towed to the ramp is hot. Backing it into cool water cools the air inside, that air contracts, and the vacuum pulls water past the rear grease seal. It does not take a bad seal, just physics and a ramp, which is why bearings fail on a schedule unrelated to mileage.
Once salt water is emulsified into the grease, the rollers and races rust, and rust ends as a seized bearing at highway speed with a boat behind. The warnings come first: a growl that changes with road speed, play when the wheel is rocked at twelve and six o'clock, milky grease at the cap, rust weeping from the hub. Warm after a run is normal; too hot to touch is a bearing telling you how much time is left.
Repacking, and what buddy bearings do not do
A proper repack is not a grease-gun operation. The hub comes apart, bearings and races are inspected, the seal is replaced every time, and the spindle checked for scoring or bluing, because a blue spindle has overheated and is finished. Bearings go back in matched sets with their races: a new cone on an old cup fails early. Preload is set by hand, then backed off to finger tight before the cotter pin, because over-tightening kills new bearings as fast as water does.
Spring-loaded pressure caps, commonly called buddy bearings, hold the hub pressurized so water is not drawn in. They help, and they are not a substitute: grease through a zerk pushes new grease in without flushing the old out, shows nobody the races, and over-pumped blows the rear seal onto the brakes. Plan on a full repack at least annually for a salt-launched trailer, sooner for weekly use, with a marine-grade water-resistant grease. Thickeners are not all compatible, so a hub gets one product, not a blend.
Surge brakes: the actuator is usually the problem
Most boat trailers use surge brakes: when the tow vehicle slows, the trailer's momentum pushes the coupler against a master cylinder inside the actuator, applying the brakes hydraulically. There is no controller in the truck, so nothing warns you until it stops working.
| Symptom | Likely cause |
|---|---|
| Trailer pushes the truck at every stop | Seized actuator slide, low fluid, air in lines |
| Brakes drag, or will not back up a ramp | Reverse lockout solenoid or mechanism failed |
| One wheel hot, one cool after a tow | Seized caliper or cylinder, collapsed flex hose |
Brake fluid is hygroscopic, so on a submerged trailer it takes on water and corrodes the system from inside while salt attacks it from outside. Fluid is replaced, not topped. Steel lines rust from the outside in and are commonly replaced with coated or stainless line here, as are rotors and calipers. Florida sets a gross-weight threshold above which trailer brakes are required.
Lights, grounds, and green wire
Water enters a cut wire end and corrosion wicks up inside the insulation, so the wire looks perfect and reads open. The repair is cutting back to bright copper and joining with adhesive-lined heat-shrink connectors on tinned marine wire. The ground causes most of the behavior that makes no sense. If the brake lights flicker the markers, or the turn signal pulses the running lights, the circuit is backfeeding through a poor ground. The white ground needs a dedicated run to clean frame metal and a ring terminal at each housing; the ball and coupler are not a ground. Incandescent bulbs are the other half, since hot glass dropped into cool water fails sooner or later, which is why sealed LED lamps on a submersible harness are the standard repair.
Tires, bunks and rollers: the parts that fail while parked
Special Trailer (ST) tires are built with stiff sidewalls to carry vertical load, not to cover miles, and they fail from UV, ozone and heat rather than tread wear. Read the DOT code on the sidewall: the last four digits are the week and year of manufacture, so 2621 is the 26th week of 2021. Replace at five to six years regardless of tread. Check the spare, run ST tires at the cold pressure on the sidewall, and recheck lug torque fifty miles after a wheel change.
Carpeted bunks hold salt and grit against the gelcoat, and staples or screws that have backed out score a hull the length of the bunk on the next retrieve. Bunk boards rot from the inside out; the tell is a fastener that spins or a board soft where the bracket bolts through. Roller trailers add flat-spotted rollers and seized shafts. On both, position matters more than parts: a hull carried on the wrong spots rather than under its stringers takes load it was never designed for. If the outboard is stuck up too, see trim and tilt repair: towing an engine that will not come down loads the transom the wrong way.
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FAQs
How often do boat trailer bearings need repacking? At least once a year for a trailer launched in salt water, more often for a boat that goes in weekly. Mileage is close to irrelevant; immersion is what matters. A hot hub cooling in cool water draws water past the seal, and once salt is in the grease the bearings rust whatever the odometer says.
My trailer lights work sometimes. What is wrong? Almost always a ground or a corroded wire end rather than a bulb. Corrosion wicks up inside the insulation from a cut end, so a wire can look perfect and read open. Backfeeding through a bad ground is what makes brake lights flicker the markers. The repair is clean copper, sealed connections, and a dedicated ground.
When should I replace trailer tires? By date code, not tread. The last four digits of the DOT code give the week and year of manufacture, and replacement at five to six years regardless of tread is common practice. Florida sun accelerates sidewall degradation, and a parked trailer ages its tires while doing nothing.
Do you repair the trailer frame or do welding? No. Structural frame repair and welding are not part of this service. Bearings, hubs, spindles, surge brakes, wiring and lighting, tires and wheels, bunks, rollers, winches and couplers are. A cracked or corroded frame or axle is photographed and referred out rather than patched.