Workshop: Fitting & replacing cassette sprockets
By Hilary Stone | Wednesday, October 1, 2008 11.00am
Worn sprockets need replacing, a job that usually goes along with replacing the chain. Here's how to get the sprocket cassette off and fit a new one.
If you fit a complete new cassette you should replace the chain; if not, your expensive new cassette will have a much shorter life if it even sorks at all. A worn chain will often slip on a new cassette.
If spare sprockets are available, it can often be economic to just replace the more heavily worn sprockets, which are generally the smaller ones. However, if your cassette has seen quite a few thousand miles it may be cheaper to replace the whole cassette together with the new chain.
Time: Replacement 15mins
Tools: Chain whip, lockring tool, Allen keys - 1.5mm if dismantling some Shimano cassettes
Before you start
Your cassette must be correctly spaced for your system if all the gears are to index correctly. If you're buying a complete replacement cassette this isn't an issue, but if you're making a custom combination you'll need to keep it in mind. More on this later.
Campagnolo 8-speed cassette sprockets are spaced at 5.0mm, 9-speed at 4.55mm, and 10-speed at 4.12mm.
Shimano 7-speed cassettes are spaced at 5mm, 8-speed at 4.8mm, 9-speed at 4.34mm and 10-speed 3.95mm.
Cassettes which do not group sprockets together on spiders can be customised using either sprockets from other cassettes made by the original manufacturer or from Marchisio. Shifting performance may suffer a little when mixing sprockets from different cassettes, as the shift gates will not necessarily be in the optimum position.
You will need to experiment to see what you are prepared to put up with. As long as you keep the sprocket spacings correct it will normally be acceptable.
Wheels Manufacturing makes spacer kits (around £20) to respace any Shimano or Campagnolo cassettes from 5mm to 4.8mm, 4.55mm and 4.35mm spacing and vice versa, as long as none of the sprockets are mounted on a spider. Sturmey Archer sprocket spacers can also be useful when respacing a cassette.
1 Lockring tool fitting
Undo your brake's quick-release and then remove the rear wheel by opening the wheel's quick-release lever. Remove the wheel's quick-release from the hub by unscrewing the knurled nut on the opposite end to the lever. Slide the correct lockring tool into place and check that it is properly engaged in the splines. Refit the quick-release without its conical springs and tighten sufficiently so that it will keep the lockring tool fully seated in the splines of the lockring.
2 Loosening the lockring
With the wheel vertical, place the chain whip on the left side of one of the larger sprockets. It should be positioned so that its handle is just above the horizontal, make sure that the chain is securely wrapped around the sprockets' teeth and that the short piece of chain on the chain whip is also fully engaged. Put a little pressure on the chain whip's handle to tension the chain. Fit a large adjustable spanner to the lockring tool so that its handle is horizontal, or just above, on the right hand side. Push up on both the chain whip and adjustable spanner firmly. The lockring should loosen easily. Take care not to let the chain whip slip.
3 Removing the cassette
Remove the wheel's quick-release. With the lockring tool, loosen the lockring completely and remove it. Lift off the sprockets and lay out all the sprockets and spacers in the same order as removed on your bench. Even with cassettes where sprockets are grouped together on aluminium carriers or spiders, there will often be spacers between the carriers. It is very important that the spacers are replaced in the correct position.
4 Shimano cassettes
Shimano cassettes come in quite a few different varieties. With almost all seven and eight-speed cassettes, five or six sprockets will be held together by miniature Allen screws - these can be undone with the correct Allen key; sometimes it's a 1.5mm Allen key and occasionally something even smaller. The Allen screw heads can be on the front or rear face of the sprocket group. The cheaper 9-speed cassettes are joined similarily. The more expensive nine and 10-speed cassettes will have sprockets mounted on spiders in groups of two or three together with spacers in between. On some Mavic hubs, spacers will need to be mounted before fitting a Shimano cassette. Spacers are also needed if mounting a 7-speed cassette on an 8/9/10spd hub.
5 Campagnolo cassettes
All current Campagnolo cassettes are 10-speed, though nine-speed cassettes are still available as spares. With Xenon, Mirage and Veloce, the cassettes are composed of single sprockets with spacers in between. With Centaur, Chorus and Record, the sprockets are mounted on aluminium carriers in groups of two or three except for the smallest three sprockets. The sprockets must be mounted so that the size markings face outwards on the freehub body.
6 Marchisio cassettes
These are available to both Campagnolo and Shimano cassette bodies and with spacers to suit 7, 8, 9 or 10-speed systems. There are two varieties - ones using adaptor pieces and ones which mount directly on the freehub body. All sprockets are single and, apart from the smallest sprocket, they are fully interchangeable. This means that you can easily customise the cassette to suit you and your riding. Unlike all the other cassettes, the size markings should face inwards when mounted on the freehub body.
7 Replacing the cassette
With all cassettes, except Marchisio, the size markings should face outwards. With Shimano cassettes, align the triangular mark on top of the cassette body with the widest spline and slide on. With the Campagnolo cassettes with sprockets mounted on aluminium carriers, align the support up with the splines on the freehub body and slide the cassette onto the freehub body. With all cassettes, Shimano or Campagnolo, it is very important to ensure that the spacers and shims all go in their correct position - it is easy to check by eye that all the sprockets are spaced identically apart.
8 Fitting and tightening the lockring
Once all the sprockets are fitted, check that the top gear-sprocket stands slightly proud of the freehub body - if not, you have missed out a spacer or shim. Fit the lockring using the lockring tool, refit the quick-release without its conical springs and tighten the lockring with an adjustable spanner until you hear or feel three or four distinct clicks. Remove the quick-release. Refit the quick-release's conical springs and refit the quick-release to the wheel.
9 Customizing your cassette
With Shimano cassettes where the sprockets are held together by Allen screws, or Campagnolo cassettes with individual sprockets, it is possible to change sprockets to build a cassette with custom ratios. With a vernier calliper, first measure the width between the centreline of the sprockets on your existing cassette. Build your cassette up on the hub, fitting the replacement sprockets where you wish. Try to take into account any differences in spacer or sprocket thickness as you go by using appropriate spacers to keep the inter-sprocket width the same. Once all the sprockets are fitted, check that the top gear-sprocket stands slightly proud of the freehub body. Fit the lockring and tighten as described in step 8.
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