How To: MTB Cassette Replacement Made Easy!

Modern chains are almost always equipped with a master link. To open it cleanly, it is best to use a pair of master link pliers. Chains without a master link can be opened with a chain tool. However, if the cassette is worn, the chain is usually worn as well. Since you are going to throw away the chain after removing it anyway, you can simply break it with bolt cutters. But be careful: the chain is under tension, so you should fix it in place – or release the tension from the rear derailleur (only possible with the SRAM "Cage Lock” function; with Shimano you can at least reduce the tension of the cage).

Tip: Break the chain on the lower run! An old spoke bent at both ends is very helpful for holding the chain’s tension until you can use both hands again. You can learn how to replace your chain here.

To remove the cassette, you must first remove the rear wheel. Loosen the axle and take off the wheel. Make sure to shift to the smallest sprocket beforehand!
Some hub manufacturers use exchangeable axle end caps to adjust the over locknut dimension or the axle diameter. These end caps are often just plugged on and come off easily. If this is also the case with your rear wheel, take the caps off and put them safely to the side.

Tip: Also place the axle in a secure and clean spot within reach of the wheel – this makes assembly easier later on.

To remove the cassette, you need a chain whip or cassette pliers as well as a cassette removal tool (this is the name of the multi-tooth socket that you can insert into the front of the cassette). This is because releasing the cassette works in the direction of the freehub. The photo illustrates how you use the tools to loosen the cassette. The cassette remover is on the front of the ratchet. To loosen the lockring, turn the remover anticlockwise while holding the cassette with the chain whip (or cassette pliers).
After removing the lockring, you should be able to pull off the cassette. If you have been riding the cassette for a long time, it may be very tight on the freehub and you may need to apply a little more force to pull it off. Make sure that you don't pull the freehub off the hub body along with the cassette! With some models this is quite easy. With the combination of an aluminium HG freehub and a cassette with individual steel sprockets, it can happen that the sprockets have eaten into the freehub and the cassette is therefore extremely difficult to remove.

Pro Tip: When loosening the cassette, bend over the wheel from the other side – as shown in the picture. This way you can't get your knuckles caught on the spokes.

Before you put on the new cassette, you should clean the freehub thoroughly. Places that you cannot reach with a rag can be cleaned with an old toothbrush.
To prevent the above-mentioned seizing of the cassette on the freehub, you should grease the freehub body a little before sliding on the new cassette.

The cassette only fits on the freehub in one position. This is ensured by grooves with varying widths at different points on the freehub body. On the cassette you will of course find splines that correspond to the hub’s grooves. Just make sure that you push the widest spline onto the widest groove.
The grooves on XD freehubs from SRAM look slightly different: they do not extend across the entire width of the freehub; the cassette is only carried along by grooves on the last piece of the freehub. The cassette is simply pushed onto the freehub from the front and screwed tight.
With high-quality cassettes, all or almost all sprockets sit on a carrier with a wide base; with cheaper cassettes, the sprockets are installed individually and separated by spacers. When you take such a cassette out of its packaging, the sprockets are usually on a plastic cylinder. You can use this as a guide to slide them on, so you won’t have to put the small sprockets on the freehub individually.
The cassettes on XD freehubs have no lockrings; the receptacle for the cassette remover is integrated. The cassette is screwed directly onto the freehub. Shimano cassettes require a lockring, which you should tighten to the torque specified by the manufacturer. Always follow the manufacturer's instructions for precise torque values.

Finally, you have to mount the rear wheel again. To do this, you should first remove old grease from the axle and apply a fresh layer. Before putting the rear wheel back on, prepare the greased axle. If you removed the axle end caps when taking off the rear wheel, don't forget them when putting the wheel back on!
You can then fit the new chain and get back on your bike. Have fun on your next tour!