Be sure as you repack your bearings that you keep all the parts from each wheel separate from the other. If any of your bearing parts are damaged and you need to replace them, about $100 to do both sides. Be sure to take your old parts with you when you seek replacements for them. Below are brands/numbers others have found and used. Your's may be different.

• Outer bearing assembly: Timken 09067
• Outer bearing race:       Timken 09195
• Inner bearing assembly: Timken 15123
• Inner bearing race:       Timken 15245
• Inner seal:                   Chicago Rawhide CR 16811
• or National 440265 S6C or GW-240-144-6 or NAPA 16811
• Amy found these worked for her 1976 JS715:
  • Western Auto: Auto Extra brand. The SKU is 713602184329 The package says it replaces: FM 442251/SKF 17146. 
    
    
• Threaded Dust Cap replacement
• Bearing Tips
  
  
• How to repack your bearings - with video (thanks Ray & Don)

Park trailer on a flat level location where ground is firm.
Block your tires and loosen the lug nuts.
Lower your trailer tongue as far down as it goes.

Place jack stands under both metal rails behind the tires.
An SUV version that will raise 21" is recommended, but not necessary.

Place your jack under one rail and jack up as high as it will go and then
raise your jackstand up to that level. Do the same on the opposite side.

When you have both wheels well off the ground, raise your trailer tongue
back up to level the trailer, which will raise the wheels even higher
and allow the axle to drop so wheels may be removed.

Finish removing both wheels, but be sure to keep all parts separated, by wheel.

Unscrew the dustcap. If you have to use channel locks to loosen,
be careful, they may be only plastic!

Clean off the grease to expose the cotter pin.
Straighten it out and remove it.

Now, remove the bearing nut.

Gently pull the hub towards you, which allows the outer bearing
to move forward. Be careful not to allow the bearing to drop on the ground.
Push the hub back and remove the bearing and the washer.

Remove the hub and place it, backside down, between two pieces of lumber.
Using a hammer and a wooden dowel, catch the back edge of
the inner bearing and tap it lightly until both it and the seal come out.

Inner bearing and seal removed.

Remove as much of the old grease as possible using a rag or paper towel.
Then place all the removed parts into a can (coffee can works great) and pour
solvent (gasoline will work, just be careful!) over them.
Let them sit a few minutes and using a brush, thoroughly clean all the parts.

If you have a compressor, use it to blow out the bearing to
assure all old grease is removed. If you don't have one,
just be sure the grease is gone.

A cleaned bearing!

Check your inner bearing seal to be sure it shows no damage.
If it does, it will have to be replaced.

Both sides should be clean, with no gouges or scrapes.

After cleaning both the inside and the outside of the hub,
use some of your grease to grease the inside of the inner hub.

Now put a walnut-sized lump of grease into the palm of your hand
and work it, from the bottom, into the inner bearings.
The grease should be pushing out the top of the bearing when it is fully greased.

When the bearing is fully greased, insert it back into the hub
and then lightly tap the seal back on.

Now, turn the hub over and grease the inside of the outer hub.

After cleaning the spindle (where hub was removed from) completely,
place the freshly greased hub back on it.
Grease (repack) the outer bearing the same way you did the inner
and then place it back into the greased outer hub, followed by the washer.

Now, replace the bearing nut.

1. Snug the nut all the way down and spin the hub around several times. Then back the nut off one of the notches in the nut, and replace the cotter pin. It is probably best to use a new cotter pin, and not reuse the old one which you removed.
2. Replace the cleaned dust cap.
3. Replace the wheel and finger-tighten the nuts.
4. Lower the trailer by reversing the steps used in raising it.
5. Tighten your lug nuts and you are good to go for another 10,000 miles!