Freehub Body Removal

Cassette hubs usually have a removable freehub body. There are a few instances when you might need to remove or replace one, so I'll show you how. First remove the axle and ball bearings (described here). Next you'll need either a long arm allen key or a hex socket bit (10mm for Shimano hubs):

Stick the tool into the freehub and unscrew it counterclockwise. These can be on there pretty tight, so don't be surprised. Once it's broken loose, remove the hollow bolt and the freehub body together:

Here is the bare hub shell, showing the splines that transfer your pedaling force to the wheel:

And here are all the pieces that you removed from the wheel:

The hub goes back together the same way you took it apart. This is a good time to clean the bearings and reassemble them with fresh grease. You might want to replace your freehub body if you try to pedal forward and your pedals just spin without turning the wheel. You would also want to replace it if you upgrade an old 7 speed bike to 8, 9, or 10 speed, since newer cassettes don't entirely fit on shorter 7 speed freehub bodies.