drakesdemise… and anyone else
You will need a pair of bearing seals for this(about $5)
To inspect your bearings, use a screwdriver to pull off the dust cap or bearing buddies… whatever your trailer is equipped with.
Before going any further, try to twist and torque the wheel to see if you have any play, or any noise when you freely spin the tire(there should be none).
Use a pliers to straiten out and pull the cotter key, and a wrench to take off the castle nut(large nut with grooves). The castle nut often will spin off by hand. If there is a washer behind the castle nut, remove that too and set everything on a CLEAN rag, you dont want any dirt going back into the assembly.
From there, gently pull out on the tire about an inch, and push it back in, you should be able to slide off the outer wheel bearing sitting in plain view and set it on your clean rag with the rest of the parts, be sure to make a mental note that is the outer bearing, some are different!
After removing the inner bearing, grab the wheel with both hands and pull while trying to keep it on center so you dont beat up the threads on the spindle(where castle nut was). The wheel should come off without too much problem.
Lay the wheel on the face(lug nut side), and grab a pair of pliers or screwdriver and pull, or carefully pry off the seal in the rear. Once it is off, the inner bearings will be exposed. Pull the bearing out and set it on the rag.
Now everything is out(for inspection). You will want to use a rag to clean these bearings off the best you possibly can. If need be, use some alcohol or something similar to get off all the old nasty grease. Once you get all the grease off, look at each bearing closely for any type of wear, uneven wear, rust, chips, pitting, or excess play in the bearing itself. If something doesnt seem right, replace it.
After you inspect the bearings, wipe all the grease you can off the bearing races inside of the hub, the races are a steel ring with a slight taper the bearings rest on. Look for any wear, pits, rust, scratches, etc.. they should be perfectly smooth with well defined edges. If there is any damage, even if it looks minor, replace them.
To remove the bearing races, you will need a hammer and a punch with a blunt end(pointed end wont work on most). Lay the wheel on the ground and tap them out gently by moving the punch position around the race while you tap it out so it doesnt bind. To install the race, coat the outside lightly with fresh grease and tap it in all the way to the seat inside of the hub(wont go any further).
On the inner bearing, if the race is still good, or you replaced it… grab some marine grade wheel grease and load the bearing up the best you can before installing it, squish the grease into every possible part. Before installing the bearing, you can also manually put a load of grease into the hub on the inner race to assure grease gets everywhere when repacked. Put the inner bearing into the race, and gently tap a NEW seal into place on the inside of the hub. This will hold your inner bearing in place, and assure you of no leakage in the near future.
Once the inner assembly is together, slide the wheel back on the axle as far as it will go, rotate the tire some and wiggle it to be sure it goes all the way on.
Now the wheel is sitting on the axle, get globs of grease and keep forcing it back into the vacancy between the axle and the hub until you cant fit anymore. Once you get to that stage, pack the outer bearing with grease just like you did the inner bearing, make sure everything is well covered with fresh grease including the bearing race. Slide the bearing into place, install the washer if there is one, and put on the castle nut.
This is the MOST IMPORTANT part… when installing the castle nut, its recommended to use a wrench about 12″ long to avoid over tightening. Tighten the nut down slowly when you start to get any pressure, rotate BOTH directions and wiggle the tire to be sure it has set to where it needs to be. Tighten the nut until you start to get a little bit of tension while spinning the wheel(binding), from there back the nut off 1/16 – 1/4 turn until the cotter key lines up in the pilot hole. Put the cotter key in, and the dust cap/bearing buddy on and you are done(if bearing buddy, pack a little more grease in until plate starts to rise).
IF by chance the wheel doesnt go back on as far as it should, its likely a bearing race isnt in place, or the seal hasnt positioned itself on the axle properly yet, do not try to force it.
I cant stress enough if the grease looks muddy, or dirty at all, be sure to get all of that old grease out of there or it will destroy your bearings.
The whole process usually takes about 45 minutes, a couple bearing seals($5), and a tube of grease. I use the grease from my grease gun(marine grade) for the job rather than the can. A total expense of $10 or less and a short period of time is way better than disaster roadside.
cheers 
First thing was that I didnt replace the rubber bearing seal that had a hole in it and it filled with water and they got scorched, being that I was out of town I had to pay somebody else to do the work and they overtightened the nuts and it poped the back seal out on the way home 
…..so I had grease everywhere outside the hub(in the brake drum) and hot dry smoking bearings on the inside 
