The short version
- On a trailer you have an option cars do not: swap the entire hub, pre-assembled.
- That turns a bench job into a twenty minute roadside repair for not much more money.
- Replace rather than repack once you find pitting, scoring or any grit in the grease.
- Never fit a new cone against an old cup. They wear as a matched pair.
A trailer wheel bearing replacement is mechanically simpler than the same job on a car. It also comes with a shortcut worth knowing before you start.
Trailer hubs are standard parts sold as complete assemblies, which is why the pricing works out oddly. That changes what the job can be.
Replace or repack?
The first decision, and the grease answers it.
| What you find | Verdict |
|---|---|
| Grease darkened but smooth | Clean, repack, carry on |
| Any grit you can feel | Replace |
| Milky or pale grease | Replace, and find the water |
| Pitting or scoring on rollers or cup | Replace |
| Blue or straw discoloration | Replace, and find the heat |
| Any roughness turning by hand | Replace |
Reading the grease properly names the cause as well as the verdict, and the used grease page covers it.
Inner and outer have shared the same water, heat and miles. Replacing one and reusing the other means doing the job twice.
The parts are cheap and the hub is already apart, so the extra cost is trivial against a second strip down.
The complete hub option
This is the trailer specific route, and most people do not know it exists.
You can buy a complete hub, pre-assembled with bearings, races, seal and often studs. It arrives ready to slide onto the spindle.
The premium over loose bearings, races and a seal is often modest. What you get back is significant.
| Rebuild your hub | Fit a complete hub | |
|---|---|---|
| Where the work happens | Bench, with tools | At the wheel |
| Races need pressing | Yes, driven in and out | Already fitted |
| Realistic time | An hour or more | About twenty minutes |
| Doable at the roadside | No | Yes |
A pre-assembled spare hub in the tow vehicle turns a failed bearing from a recovery call into a twenty minute stop.
It is the most useful thing you can carry for a trailer, and it costs little more than the loose parts.
The job, rebuilding the hub you have
- Chock, jack and support the trailer properly, then remove the wheel.
- Pull the dust cap, straighten and remove the cotter pin, then take off the castle nut and washer.
- Rock the hub so the outer cone drops into your hand, then slide it off the spindle.
- Lever out the seal and remove the inner cone. Both go in the bin.
- Drive the old cups out from behind, working evenly around them so they come out square.
- Drive the new cups in square and fully seated against their shoulders.
- Pack both cones, fit the inner one, then fit a new seal square and the right way round.
- Refit the hub, the outer cone, the washer and the nut, then adjust.
The packing technique and adjustment sequence matter more than the rest. Both are on the repacking guide.
The two mistakes that cause repeats
Mixing new and old. A cone and its cup wear into each other as a matched pair. A new cone on an old cup runs on a used wear pattern and fails early.
Not seating the cups. A cup driven almost far enough leaves the bearing proud, so the adjustment is wrong from the start. No amount of nut fiddling fixes that.
Run a fingernail along the spindle where the cones sit and where the seal rides. Any groove, score or blue tint means the spindle itself is damaged.
A damaged spindle chews through the new bearing, and no amount of new parts on top helps.
What to buy
Trailer bearings are standard industry parts, identified by number rather than by trailer make.
Read the numbers stamped on the cones and cups you remove, and buy exactly those. Capacity charts are a starting point, since a previous owner may have changed an axle.
Buy cones and cups together, a new seal every time, and a new cotter pin. The numbering system is on the sizes page.
Boat trailers specifically
Everything above applies, plus one thing that does not affect road trailers.
Launching puts a hot hub into cold water, and the trapped air contracts as it cools. That pulls water past the seal, however good it is.
So boat trailer wheel bearing replacement is driven by immersions rather than miles, and a pressurized grease cap is worth fitting. The trailer section has the figures.
Finishing
Adjust to a barely perceptible play rather than a torque figure. Seat while rotating, back off fully, retighten finger tight, then back off to the nearest cotter pin hole.
Fit a new cotter pin and a clean dust cap. Then drive a short distance and feel each hub, comparing all of them.
Warm is normal. One hub noticeably hotter than the others means stop and recheck the adjustment.
With drums or discs fitted the sequence changes slightly, and the brakes page covers the extra steps.
How towing loads the tow vehicle is a separate question, answered on the towing page.
Which grease suits a boat trailer is on the marine grease page, an RV is on the RV grease page, and the oil filled alternative is on the oil bath page.
Which grease goes back in, and how to read the bearing number before ordering, is on the trailer grease page.
Trailers that get launched are their own case, and the mechanism behind it is on the page about why the ramp destroys hubs.
Common questions
How do I do a trailer wheel bearing replacement?
Remove the hub, drive out the old cups, drive in new ones square, pack and fit new cones with a new seal, then adjust to a slight end play. Or fit a complete pre-assembled hub instead.
Should I replace or just repack?
Repack if the grease is smooth and the surfaces are clean. Replace if you feel any grit, see pitting or scoring, or find discoloration from heat.
Is a complete hub worth buying?
Often yes. It removes the pressing work, cuts a trailer wheel bearing replacement to about twenty minutes, and makes a roadside repair possible.
Do I need to replace both bearings?
Yes, in practice. Inner and outer have shared the same water, heat and mileage, so replacing one and reusing the other means doing the job twice.
Can I reuse the old cups?
No. Cones and cups wear as a matched pair, so a new cone on an old cup runs on a used wear pattern and fails early.
What if the spindle is scored?
Then the spindle needs attention, because it will destroy the new bearing. Check it with a fingernail before fitting anything.
How tight should the nut be afterward?
Not tight. Seat while rotating, back off fully, retighten finger tight, then back off to the nearest cotter pin hole for a slight end play.