Bearings are the unsung heros of every wheeled conveyance. Because they are hidden from view, encased in grease and disguised by pretty wheel covers, bearings go largely unnoticed for the job they do. And yet, it is the wheel bearings that handle the load of the trailer and make high speed road travel possible. Bearings must resist lateral forces as the trailer is tugged in different directions by the bike, and it’s the bearings that really take the pounding when a trailer tire finds a hole to drop into or runs over an obstacle in the road. Tires may be where the rubber meets the road, but bearings carry the biggest part of the burden and get the job done.
Trailers using typical lightweight axles have two-piece caged bearings that are packed in grease and are set between the wheel hub and axle. As the wheel rotates the hub, the bearings spin around the axle. Trailer bearings are made of hardened steel and will usually last for the life of your trailer when they are properly maintained. Opinions about what constitutes proper maintnance varies widely, so I’ll try to offer you a reasonable maintenance schedule that should suit the widest range of trailer users.
The most important aspect of bearing maintenance is to keep bearings well encased in fresh axle grease. Axle grease prevents metal-to-metal contact, absorbs heat from the friction generated by the spinning bearings, and prevents moisture from getting to the bearings. Since bearings are made of hardened steel, they will rust overnight if exposed to water. Over time, even heavy axle grease tends to break down and wear out, providing less lubication and allowing moisture to creep in.
Wheel-on Bearing Inspection
You can check your wheel bearings any time simply by observing how the wheel feels when you rotate it. This is something you should do at least once a year and preferably each time you plan to take a trip. Wheel bearings should display no visible play, meaning, if you grab the top of the wheel, push in and pull out, the wheel should not move. Likewise, with two hands, grab the tire and the nine o’clock and three o’clock positions and try to turn the wheel in and out like the front wheel of your bike. Again, you should feel no movement in the wheel. If you do, it’s a sign your bearings are worn and should be replaced immediately. Jack up one side of the trailer and spin the wheel. It should turn freely with no grating sounds. If you find the wheel won’t make at least one complete revolution or you hear any grinding noise, you’ll need to pull the bearings for further inspection.
Wheel-off Bearing Inspection and Service
Many trailer manufacturers recommend that you check your trailer bearings and repack the grease annually. If you’re so inclined, there’s no harm in that, but it probably isn’t necessary. If you pull your trailer a few thousand miles per year or less, you can probably go several years between wheel-off inspections. If you trailer between five and ten thousand miles per year, expect to repack the bearings every three years or so to keep them in peak condition. For those who trailer more than ten thousand miles per year or frequently trailer in extreme conditions—rain, bad roads, dusty conditions—you are a candidate for annual bearing inspection.
Wheel-off maintenance entails disassembling the wheel hub, pulling out the bearings for visual inspection, cleaning and repacking them with grease. It isn’t difficult, and it’s a good thing to know in case you run into trouble on the road. If you don’t care to do this, a mechanic can do this for you.
Begin by removing the dust cap. Use a hammer and cold chisel to pop the cap off. Don’t use pliers to pry off the cap, you will dent the cap and possibly compromise its ability to seal. Remove the cotter pin that holds a castellated nut in place. Now remove the nut. This will allow you to remove the wheel hub from the spindle.
Remove the bearings
With the bearings removed, wipe everything in the assembly as clean as possible including the inside of the wheel hub, the spindle, and the bearings. Opinions differ whether to soak the bearings in solvent to remove all the grease. I think it’s not necessary because solvent may find places to hide that will attack the new grease you put in. I think it’s better to simply wipe the bearings as clean as you can get them and call it good.
Run your fingers over the bearings, feeling for any hesitation in their action. Examine them for rough spots or pitting on the surfaces. Bearings are not expensive, so if you find any problems, replace them with a new set.
Packing bearings is fun and messy. Place a glob of grease in the palm of your hand and work it into the bearing assembly until the whole package is packed with grease.