Fix Your Bike. Grease Your Bearings and Change Your Freewheel.

Most people don't realize this, but your bike needs maintenance. Your axle bearings needs to be cleaned and repacked with grease every 500 miles (100 on a mountain bike).
This instructable shows how to repack your axle bearings and install a new freewheel body (if you need one).

If you don't know how to do this much already, this may be too big a job for you at this point.

Remove the quick-release skewer from the axle. Take care not to lose those tiny springs.

You'll need a special tool to remove the cassette from the hub. $6 at a bike shop. You'll also need a wrench to turn the tool.

Finally you'll need a chain whip or cog holder to hold the sprockets in place while you unscrew the cassette retaining nut. Once removed, the cog stack will slde off the freewheel body effortlessly.

Here is the freewheel body and axle in place.
First remove the jam-nut and washer from the axle then remove the bearing cone nut. This holds the bearings in place.

See the bearings within. Remove the bearings and clean everything till it is absolutely spotless. Aerosol brake parts cleaner works very well for this and only costs $1.99 at your local auto parts store.

If you're just greasing your bearings, SKIP THIS STEP!
Insert appropriate sized allen wrench into freewheel body and unscrew. Set aside the old freewheel body and place the retaining bolt with all the other stuff you need to clean.

Clean the cogs, axle, cone nuts, washers, jam-nuts and especially the interior of the bearing cups in the hub. If you see any residue of any kind, you need to clean some more.

Unwrap the new part. View the instructions and take whatever action you see fit. Personally, I found the instructions insulting. They essentially said: "Be sure to install the part correctly." in 8 different languages, but didn't say exactly HOW to do it.

I recommend Marine Axle Bearing Grease for your bearings. It's for boat trailers and is available cheap at your local auto parts store.
Apply a generous coating of grease to all the mating surfaces like the steel washer between the freewheel body and the hub and the freewheel locking bolt.
Replace the freewheel body and tighten the locking bolt.

Load up the bearing races with generous helpings of marine axle grease. Load both sides with grease before you replace the bearings. The grease will hold the bearings in place.

Load the bearings into the brake side first and insert the axle. The axle will help hold the bearings in place. On the opposite side, place the axle part way into the hub and load the bearings into the cup area. Once all the bearings are in, push the axle the rest of the way in. Next replace the cone nut that holds the bearings in place.
Finally, tighten the cone nut until you feel some binding then back off the tension until the wheel spins freely with no binding or rough feeling. Finally add the washer and jam-nut and tighten it all down. If it starts binding, loosen it up a little.

Notice there is one small groove on the freewheel body. There is a corresponding slot in the cog stack. This ensures that the cog stack can only go on one way. Replace the cog locking nut.

Replace the quick release skewer. Note that the springs are cone-shaped. The big end faces away from the hub.
You're now ready top replace the wheel on the bike.