Many trailer manufacturers recommend this maintenance every year if your trailer gets normal use, or at least every 20,000 miles. To do this job, you'll need a jack, a pair of jack stands, a large screwdriver, a hammer and a needle-nose pliers, clean rags, a small pan, about a quart of kerosene and a spray can of brake cleaner.
First, loosen the lug nuts on one wheel and raise the side of the trailer with a jack. Support the trailer with jack stands and then spin the wheel and listen to the bearings. If the wheel spins freely and quietly, proceed with repacking the bearings. If you hear friction or a growling sound, you most likely have a bad bearing or spindle. If this is the case, take the trailer to a service center to get the bearings replaced.
Figure A: Typical trailer hub assemblyNote: You can download and print Figure A from the Additional Information section below.