Compared to the screw-on freewheels of yore, cassette sprockets are easier to remove and replace.
There are a few reasons why you’d want to do this.
- As your chain wears down, it wears the cassette and chainrings along with it. If you use a chain wear indicator, a chain is usually replaced when it displays 0.75% stretch. Following this logic, a cassette is usually considered ready for replacement once its third chain wears down.
- Different terrain calls for different gearing, hence different cassettes. Close-ratio cassettes, such as an 11-25T unit, are useful for riding over flat areas and in closed-course criterium racing, the smaller steps between cogs offering better cadence control. Wide-ratio cassettes, such as a 12-30T unit, come into their own when climbing steep hills. Note that this change of cassettes also requires a resized chain.
- Most frequently however, removal of the cassette allows you to clean it off the bike without affecting the grease inside the rear hub and freehub body. While a grimy cassette can be cleaned while installed, excess degreaser can eat the grease in places that you need it. This will be our subject for today.
Whichever your reason, you will need a couple of specialist tools for this job. You will need a cassette lock ring tool and a chain whip. The chain whip is there simply to counteract the freehub’s one-way rotation while you unscrew the lock ring off the top of the cassette. In addition, you’ll usually need an adjustable wrench to actually turn the lock ring tool.
To start with, remove the quick release skewer from the wheel. Make sure you slide both the end springs on the skewer so you don’t lose them, then thread the end nut back on. Many lock ring tools, such as my Shimano TL-LR15, have a locator pin that goes into the axle where the quick release skewer would normally be, so slide the lock ring tool into the axle and make sure it’s inserted as far as it will go.
I find it best to stand over the rear wheel with the cassette facing away from your feet. Hold the chain whip in your left hand, and wrap its links around one of the larger cogs on the cassette. Now take the adjustable wrench in your right hand and put it in around a 30-degree angle to the chain whip, then push hard on the wrench to break the lock ring loose. It may take some effort, as most lock rings are held on with 40 Nm of torque.
Once the lock ring is loose, unscrew it all the way off. Now you can slide the cassette off the freehub body.
CLEANING THE CASSETTE AND FREEHUB BODY
If you’re cleaning the cassette, put it in a bowl, apply degreaser, and leave it for a few minutes. You’ll find that it’ll do a lot of the work for you. Take a brush and scrub off whatever the degreaser missed.
Once done with the degreaser, make sure the cassette is dry. Take an old rag and floss it in between the pinned cogs of the cassette. This will also lift any dirt stuck in between.
It’s worth paying attention to the condition of the freehub body, as it’s the unsung hero of your drivetrain, directly turning the rear wheel. You’ll find that the cassette cogs can bite into the splines of the freehub body. This is normal wear and tear. Apply some degreaser into a rag and wipe it clean.
The cogs all just slide onto the freehub, but they’re keyed by the splines such that they will only go in one specific way. One spline on the freehub body is thinner than the others, and that’s the key.
In case you have free cogs in your cassette, they are engraved with the number of teeth they have on one side. Remember that this side always faces outward. Finally, the smallest cog usually has serrations on its face that the lock ring will bite against.
Before screwing the cassette lock ring back on, apply a bit of grease to the threads. This will make it easier for you to unscrew the lock ring in the future, and prevent corrosion from seizing it shut on the freehub body.
Now put the lock ring onto the cassette and screw it in by hand using the lock ring tool. For the final tightening, you don’t need the chain whip any more. The lock ring usually has its recommended torque engraved on it, and it’s usually 40 Nm. Take your adjustable wrench and turn the lock ring until it clicks into place.
Finally, return the quick release skewer into the axle. You’re done!
I hope this helped you. Let me know what other bicycle maintenance tips you’d like to learn about by leaving a comment below.