The freehub is one of the components on the bike whereby almost no maintenance is done at all. This is because it hardly gives any problems, and usually lasts very long, unless you are a hardcore cyclists who rides hard for long distances, clocking up lots of mileage!
After a series of freehub failures experienced by Matt and KC, it has highlighted the fact that freehubs do fail, although it is quite rare! In both the cases, I believed the springs holding the pawls in the freehub broke, causing the hub to freewheel in both directions.
Note that freehub maintenance is not a routine maintenance at all, and one should not attempt it unless you know how to put it back! Usually hubs with sealed bearings are easier to take apart and re-assemble, as compared to cup-and-cone bearing hubs.
The inside of the freehub! Note the ratchets that will engage with the pawls on the freehub body. This is the degreased condition.
The other parts of the rear hub. The freehub body and the covers/axle support on both sides of the axle. I'm lucky that this hub (PZ Racing) is maintenance-friendly.
The 3 pawls on the freehub body, degreased. Not with degreaser, but just wipe off the old dirty grease.
Special grease for the freehub! More viscous than oil, but not as thick as normal grease. This is something like a light grease.
Grease generously! Make sure to get grease under the pawls on the freehub body.
After greasing, the freehub runs much smoother, but it is also less noisy as the grease somewhat cushions the snapping of the pawls onto the ratchet. As the hub runs, the grease will move around and the hub should get louder over time.
By greasing the internals of the freehub with fresh grease, it helps to ensure that the wear and tear is kept to a minimum, and this will help to extend the life of the freehub.