The cassette is one of those bits that doesn’t get a great deal of ongoing maintenance. You fit it, use it until it’s worn out, and replace it. With adequate cleaning and lubrication they can last for a fair while, so there’s a chance you’ve never had to change it before and don’t know where to start…
1. The first thing to do is to gather the necessary tools. There aren’t many, but you may not have a couple of them. You’re most likely to have a big adjustable spanner, but you’ll also need a chainwhip and a lockring tool.
As with all maintenance jobs, this one’s a lot easier if you clean your bike first. Once everything’s sparkly, take the back wheel out.
2. With the back wheel out, undo the nut end of the quick release skewer (watch out for the centring spring falling off), put the lockring tool into the splines in the lockring and secure it with the skewer nut. This will prevent the lockring tool slipping which isn’t ideal when your hands are near all these spiky sprockets.
3. To undo the lockring we need to turn it anticlockwise. But if you try that, you’ll notice that all that happens is that the freehub rotates. We need some way of holding the sprockets so we can get the lockring undone, and this is where the chainwhip comes in. Wrap the long bit of chain around one of the larger sprockets as shown, and pull the handle of the chainwhip down until the short length of chain engages on the same sprocket. It’s important to get this the right way round, it doesn’t work so well back to front.
4. Once the chainwhip’s in place, use the adjustable spanner to turn the lockring tool anticlockwise. It might take a bit of heft, so persevere. If you position the tools so they’re opposite each other you can push down on both of them at once.
When you’ve managed to shift the lockring, you’ll need to take the skewer out so you can remove it completely. Once you’ve got it moving you can take the chainwhip off and just hold the cassette with your hand.
4. With the lockring off, the rest of the cassette should simply slide off the freehub body. Usually the top couple of sprockets are separate, so don’t be surprised if they drop to the floor and roll off somewhere.
If you’re taking the cassette off to service the hub or replace the freehub, now’s the time to do that. If you’re refitting the cassette, give it a good clean up including down between the sprockets. If you’re replacing it, lob it in that box of bike stuff that’s actually useless but seems too good to throw away.
5. Refitting the cassette is pretty straightforward. If you’re fitting a seven-speed cassette onto an eight- or nine-speed freehub body, you’ll need a spacer behind the cassette. Otherwise the cassette just slides straight on. It’s a good idea to lightly coat the freehub body with grease (don’t go mad, most of it will be pushed out by the sprockets. The only tricky part is lining up the splines correctly. There’s one narrower spline on the freehub body and an associated narrower slot in the cassette. These have to match up or the cassette won’t fit on.
6. Most of the cassette goes on in one piece. You’ll need to put the couple of separate sprockets on, er, separately. Make sure you get them the right way round… Smear a bit of grease on the threads of the lockring and thread it into the end of the freehub body.
7. The final job is to get the lockring tool out again, fit it into the lockring and use the big spanner to tighten it up. You can again use the quick release skewer to hold the tool in place, although as you’ve got a spare hand this time (because you’re tightening against the freehub mechanism so you don’t need the chainwhip to hold the cassette still) you can usually get away without. The lockring will click as it tightens as there are serrations under the face that help to prevent it from undoing. If you’ve got a new cassette you’ll find suggested torque settings in the instructions, but chances are you don’t have a torque wrench so they’re not much use. Snugging it down with the big spanner is about right. You don’t want it coming loose mid-ride…
Once the lockring’s tightened down, replace the quick release skewer (the springs go narrow end inwards) and put the wheel back in the bike. Run through the gears on the workstand just to make sure everything’s lined up right. If it isn’t, check the back wheel’s in straight before taking everything apart again. And that’s it…