Boat trailer bearings heat up on the highway and then go straight into cold water, which BoatUS notes can draw water in past the seals. Repacking means pulling each hub, cleaning and checking the bearings, packing them with fresh grease and fitting a new seal. Here is the job, following the axle maker's own instructions.
Clean, inspect, pack, set the preload, and fit a new seal.
When to repack trailer bearings
Dexter Axle says to lubricate the bearings every 12 months or 12,000 miles. It also says axles without its E-Z Lube feature are not designed to be submerged, and their bearings should be repacked after each immersion. EZ Loader recommends inspecting the bearings and replacing the seals when the boating season is over or before storage, and checking the bearing adjustment every 2,000 miles or before every season, whichever comes first.
Bearing protectors help, but EZ Loader is clear that they are not a replacement for proper bearing maintenance.
How to repack trailer bearings
Secure the trailer and lift the wheel
EZ Loader says to hitch the trailer to the tow vehicle and block the tires so it can't move. Where to put the jack differs by maker: EZ Loader places it under the axle or the frame near the axle, while Dexter warns never to lift or support a trailer on any part of the axle or suspension. Use the points in your own trailer's manual, and never go under a trailer unless it is on jack stands rated for the load. Take the wheel off.
Remove the cap and the spindle nut
Pry off the grease cap a little at a time around its edge. A bearing protector comes off by holding a block of wood against its side, tapping the wood, then moving to the opposite side and tapping again to walk it out. Remove the cotter pin or nut retainer, the spindle nut and the washer.
Pull the hub
Slide the hub off the spindle without letting the outer bearing fall out. The inner bearing stays in the hub, held by the seal.
Remove the seal and the inner bearing
Pry the old seal out with a seal puller or a screwdriver. Dexter says never to drive the seal out with the inner bearing, which can damage the bearing.
Clean and inspect
Wash the old grease off the bearings with solvent, dry them with a clean, lint-free cloth and look at every roller. Don't spin a bearing with compressed air; Dexter says it can damage it. Check the bearing cups inside the hub: any pitting, spalling or corrosion means replacement, and Dexter says bearings are always replaced as a set, cone and cup together.
Check the spindle
Wipe the spindle where the seal rides and look for nicks or roughness. Dexter files off burrs and cleans that area with very fine emery cloth. Deep gouges there can make a new seal leak.
Pack the bearings
Put a lump of grease about the size of a half dollar in your palm. Press the wide end of the bearing into the edge of the pile so grease is forced into the rollers, and work around the bearing roller by roller until it is completely full. Then give the bearing cup a light coat.
Fit a new seal
Put the packed inner bearing in the hub, then drive the new seal in with a seal driver or a block of wood pressing on the seal's outer ring, evenly and straight, never hammering on the seal itself. On its 600 to 8,000 lb axles Dexter presses the seal flush with the back of the hub and says never to bottom it out. Follow the seal maker's note on sealant: Dexter uses a thin coat on the outside of metal-cased seals and none on rubber coated ones.
Reinstall the hub and adjust the nut
Slide the hub on, then the outer bearing, the washer and the spindle nut. Adjust the nut by your axle maker's procedure; the table below shows how much Dexter's and EZ Loader's differ. Finish with the maker's own check; EZ Loader's is a wheel that turns easily with no play when you rock the tire.
Lock the nut and cap the hub
Fit the cotter pin or nut retainer without tightening the nut past the adjusted position, and bend the pin's legs over. Refit the grease cap or bearing protector and refit the wheel.
Spindle nut adjustment, by axle maker
Each maker's own procedure, as published. Use the one for your axle; the figures are not interchangeable.
Axle
Seat the bearings
Then
Final setting
Dexter, standard grease or oil axle with cotter pin
About 50 ft-lb while slowly turning the hub
Loosen to remove the torque without turning the hub
Finger tight until just snug, then back off to the first slot that lines up with the cotter pin hole
Dexter, axle with nut retainer and cotter pin
About 30 ft-lb while turning the hub; the bearings should bind but not lock
Loosen only until the torque reaches zero, hub held still
Finger tight while turning the hub; never tighten past finger tight to fit the retainer
Dexter, E-Z Lube axle with the newer nut retainer
About 50 ft-lb while slowly turning the hub
Loosen to remove the torque without turning the hub
Finger tight until just snug, then snap on the retainer; if it is too tight, back off about 1/12 turn
EZ Loader trailers
30 ft-lb while turning the hub
Back the nut off without disturbing the hub
18 to 24 in-lb (finger tight); the wheel turns easily with no play
Bearing protectors
A spring-loaded bearing protector, such as a Bearing Buddy, replaces the grease cap with a piston that keeps the grease under slight pressure. Other designs exist, so follow the instructions for yours. Bearing Buddy says its piston holds about 3 psi so water can't get in when the hub is submerged. For it to work, the hub has to be completely full of grease.
Add grease through the fitting in the piston with a hand grease gun, never a power gun. Stop when the piston starts to move out: Bearing Buddy fills until it is about 1/8 inch out, Dexter until the piston just rocks or sits mid-travel, and EZ Loader stops as soon as the spring begins to compress. Overfilling can damage the inner seal. To check later, press on the edge of the piston: if it rocks, the hub is full; if it is bottomed out and won't move, add grease.
Bearing Buddy notes that air trapped in a freshly packed hub works out over the first few miles, so check the piston after a short drive and top it up.
How to tell if trailer bearings are bad
Rock the wheel. With the wheel off the ground, hold the tire at its outside edges and push one side while pulling the other. EZ Loader says there should be no noticeable rocking.
Spin it and listen. Smooth and silent is good. If it grinds, EZ Loader sends owners to a dealer for replacement.
Look at the cups. Pitting, spalling or corrosion inside the hub means a new cone and cup set.
Watch the seal. A film of grease around the seal is normal. Heavy leaking, or having to add a lot of grease, means a leaking seal.
What size trailer bearings do I need?
Use the bearing and seal part numbers your axle maker specifies; Dexter lists its own in a bearing and seal replacement chart. Bearing protectors come sized to the hub, and Bearing Buddy says one that won't drive in, or won't fit tightly, is the wrong size: don't force it.
Oil bath hubs
Some trailers use oil instead of grease, with a clear cap that shows the level. EZ Loader's oil bath hubs take SAE 50W or 90W gear oil filled to the mark on the sight glass; use the oil your hub maker specifies. Dark oil is normal; milky or light colored oil means water has got in, and it should be drained and replaced.
Common questions
Dexter says every 12 months or 12,000 miles, and after every immersion on axles that are not built to be submerged. EZ Loader recommends inspecting the bearings and replacing the seals at the end of each season.
No. EZ Loader says bearing protectors are not a replacement for proper bearing maintenance.
EZ Loader specifies a waterproof, lithium-based marine trailer bearing grease. Dexter warns against mixing different grease types; clean out all the old grease when you switch.
Only as tight as your axle maker's procedure says, which ends at finger tight after seating the bearings. The wheel should turn freely with no play.
No. EZ Loader and Dexter both say to use a hand grease gun; a power gun can push grease past the seal.
The wheel rocks when you push and pull on the tire, it grinds when you spin it, or the bearing cups show pitting or rust.
Specifications come from manufacturers' published documents and can change. Check your engine or boat maker's current manual before you change a setting or fit a part.