Servicing rear hubs is trickier than servicing front hubs, since the right-hand side of the axle is concealed under the cassette. It is possible to service the hub without removing the cassette, but it’s much more difficult – the bearing surface is behind the cassette, so it is tricky to clean properly. Use these steps to remove the cassette, then replace it after you’ve cleaned and regreased the hub.
Almost all cassettes use the same fitting method and the same tool, making cassettes easily interchangeable between hubs of different makes. The main body of the cassette slides over the freehub on ’splines’ – the freehub has long parallel grooves all the way around it, which fit into the identically shaped grooves on the inside of the cassette. When you pedal, forcing the chain around, the sprockets are supported all the way around by the leading edge of each spline. The cassette is held onto the hub with a lockring, that screws into the end of the freehub. Once this is removed, the cassette will slide easily off the freehub.
The standard fitting means that one tool will fit all lockrings. The tool also has a set of splines, which fit into matching slots in the lockring. The best type of tool for hollow, quick-release axles has an extra rod that extends out from the middle of the tool. This supports the tool under pressure, stopping it from slipping out when you turn it. You’ll also need a chain whip to hold the cassette still while you turn the lockring and an adjustable spanner to turn the tool. You won’t need the chain whip for refitting the cassette – the ratchet inside the freehub will stop it from turning. See the transmission chapter for more details about cassettes.
“When you pedal, forcing the chain around, the sprockets are supported all the way around by the leading edge of each spline”
- Remove the skewer completely. Fit the cassette tool over the end of the axle so it engages with the splined hole in the centre of the cassette. Seat it firmly, so it doesn’t slip off. If the tool has a rod poking out of its centre, insert this into the hole in the end of the axle. If the tool has a hole in the middle, refit the skewer and use it to clamp the tool onto the wheel. Otherwise just seat the tool firmly.
- Stand the wheel on the floor at your feet with the cassette facing away from you. Take the chain whip in your left hand. Wrap the loose end of chain around the top spocket of the cassette, so that it passes across the top of the cassette and back around the bottom, leaving the handle sticking out horizontally to your left.
- Fit a large adjustable spanner onto the cassette tool so that it sticks out horizontally to your right. Lean over the wheel and push down on both tools, steadying the bottom of the wheel between your feet. The chain whip will stop the cassette from rotating, so that the cassette tool can undo the cassette lockring. There will be a horrible crunching noise as it undoes. Don’t panic, this is perfectly normal!
- Once the lockring is loose, undo it completely. Now you can slide the cassette gently off the freehub body – the sprockets simply pull straight out from the wheel. Some of the outer sprockets are separate; take them off carefully and keep them in order, together with any accompanying washers.
To refit the cassette after servicing the hub:
- Look at the freehub body, which the cassette slides onto, and the hole in the middle of the cassette. You see there are splines on the outside of the freehub body and matching ones on the cassette. One of the splines is slightly fatter than the others. Line up the fat spline on the freehub body with the fat slot on the cassette, and slide the big chunk of cassette onto the freehub body. Fit any loose sprockets with a washer if there was one originally.
- Refit the lockring, starting it off by hand. Align it carefully – its easy to cross-thread as the thread is very fine. Once it’s too stiff to turn, refit the cassette tool into the splines and use a large adjustable spanner to turn it. It makes the crunchy noise as it tightens – again, this is fine. It still needs about a half-turn after the noise starts.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “The importance of cleaning and regreasing sealed bearings”