Re: Symptons of bad trailer wheel bearings?
Well, I disagree. When you become attuned to the normal sound of the trailer, then when bearings start to go bad you will hear them through the trailer frame and into the tow vehicle--unless you have the boom box turned all the way up. As the bearings "spall" they will start to "grumble." They won't fail immediately, but you don't have much time left either.
That is your warning and it is now time to stop before the bearings fail completely.
I do remember a time many years ago during the CB craze. I was listening to a fellow on the radio. " I have a bad bearing but I am going to try to nurse it home." No more than 5 minutes later, probably more like two, I hear: (excitedly) "Oh, Crap! The wheel fell off." He made a poor decision. He needed to leave the boat on the side of the road in either case, but when the wheel fell off, he had much more repair and expense to go through. Better to have stopped and unhitched the trailer before the wheel came off.
As others have said: Before using the trailer, jack up the wheel and spin it. it should not rumble or grind and the bearings should operate smoothly.
That said, wheel bearings in any auto usually last the lifetime of the vehicle with no repacking. Of course, they don't get dunked in water repeatedly. However, if you keep your trailer bearings repacked and seals in good condition, you may never need to replace them either.