Straighten That Shimmy- Replacing Wheel Bearings
The wheel should be propped up on a stout box so that the hub can be accessed without pressing on the brake discs. Brake discs are not meant to take side loads and will bend more easily than you think. We propped our Beta's wheel on a crate. If the wheel has a drum brake, remove the brake backing plate and clean out the brake dust with a damp cloth before removing the wheel bearings. Drum brake dust may contain asbestos so don't blow it out all over the shop with compressed air.
When the hub is warm (the hottest it should get is hot enough to touch for a moment without burning yourself -- obviously use caution around anything hot) you can flip it over and drive the bottom bearing out with a drift. The inner spacer between the bearings can move a bit inside the hub and be pushed to one side exposing the edge of the inner race. Once you start hammering on the inner race the bearing is toast -- ball bearings can't take sharp side loads and will get flat spots, ruining the bearing. So don't re-use it.After one side is out, the inner spacer can be pulled out, along with any shims. Important: Note the position and order of the parts. The other side of the hub is then heated and the remaining bearing driven out in the same manner. Neither bearing should take much force to drive out.
Once you have the bearings out, you can clean up the inner spacer parts and inspect the inside of the hub. In the case of our example Beta, the reason for the trashed bearings was obvious -- there were seals on the outside of the bearings only, the insides were wide open to any water that leaked into the hub. So they rusted. The replacement bearings have seals on both sides to prevent this.
Inserting the new bearings is the reverse of removing the old. You can put the new bearings in the freezer while preparing to heat up the hub to receive them. Heat the hub up until water sizzles when a few drops are sprinkled on the hub, then quickly drop the new bearings in and seat them with a hammer. If you don't have a bearing or seal driver, use a socket or piece of pipe of the same diameter as the outer race to seat the bearing. Pounding on the inner race will damage the bearing, requiring you to remove it again soon. Make sure that the bearing starts square to the hub and doesn't get cocked sideways as you drive it in.
Bearings are normally installed with the writing (on the edges of the races) towards the outside of the wheel, and should be seated fully against a shoulder in the hub. Yours may be different: Best to check the manual if you didn't check the bearing when you removed it.
Flip the wheel over, grease and insert the inner spacers and shims, and heat the hub to install the other bearing. You're done! Put the wheel back on the bike, tighten everything up, and you're off, more smoothly than before.