Cassette (and freewheel) Cleaning
There are two types of rear gears (and so wheel hubs) found on MTB’s;
The freewheel is a one-piece cluster of sprockets which also contains the freewheel mechanism (the ratchets that allow the gears to spin freely in one direction but not the other, thus allowing the bike to coast, or freewheel).
The freewheel screws directly (see the middle picture above) to the rear wheel hub and can be fitted easily without the use of a tool as the force of the chain on the gears will tighten the freewheel into place, just take care that the threads have engaged cleanly and screw it down by hand as far as you can. For removal, the splined tool shown in the right-hand picture is inserted over the axle (with QR removed if applicable) and into the corresponding splines in the center of the freewheel then turned anti-clockwise.
Depending on how long the freewheel has been in place and whether or not the person who fitted it used grease or anti-seize on the threads, you may find it helpful if somebody else holds the wheel for you. Keep the wheel as horizontal as possible and use handle extensions (like a breaker bar or a length of pipe) if necessary for extra leverage.
Remember to apply a little grease or anti-seize to the threads when you refit.
The most common type of rear gears on modern 8 and 9 speed MTB’s is the cassette. As the design allows the axle bearings to be placed further out from the center of the axle and closer to the frame this design is not only more robust and durable than the freewheel design, it is also typically much lighter. The cassette is usually a multi-piece unit and will most typically be like the cassette shown in the left-hand picture above (SRAM 970), comprising of a block of sprockets held together with a bolt (SRAM) or long rivets (Shimano). The two top (smallest) sprockets are separate pieces.
The XT cassette (second picture from the left), like the SRAM 990, has a 4 or 5 arm spider that the lower 5 gears are riveted to. The upper 4 gears are individual sprockets. This kind of design is much lighter than the traditional block design.
The freewheel mechanism for a cassette hub is contained within the freehub body of the rear wheel hub. The freehub body is splined to provide a good interface with the cassette. You’ll notice that one spline recess on the freehub body is broader than the rest, and that there is a corresponding broad spline on the cassette sprockets. These broad splines must be lined up before the sprockets can be mounted on the freehub. On a 9 speed freehub body, a 7 speed cassette will need a 5mm spacer. This is fitted before the rest of the gears (see the right-hand picture above).
On XT-type cassettes with individual sprockets, pay careful attention that you’re fitting them the correct way around. Each sprocket will have a number (eg. 14T, 15T) denoting how many teeth it has; the side with the number on should be facing out.
The cassette sprockets are then held in place using a lockring, tightened to 40Nm. The third picture above shows a lockring next to the fitting/removal tool.
Because the cassette is mounted to the freehub body it is not ordinarily possible to unscrew the lockring when it is correctly tightened. To enable us to remove the lockring we need to hold the cassette to prevent it from turning and for this job we use a chainwhip. It’s a great tool to have and although a good one will set you back £/$20-30 it really should be considered one of your ‘basic’ tools.
As per the pictures above, the chain whip should be fitted to one of the middle to large sprockets for best fitting and leverage. Even at the correct torque, a lockring should free up easily with a decent sized wrench. I favour a long handled chainwhip like Park’s SR-1 so that, in the eventuality of a jammed on lockring, I can rest the end of the handle on the tyre and hold it down with my weight under my knee, leaving me with both hands free to operate the lockring tool and wrench. Depending on how tight the lock-ring is fastened (or attached with rust/crud on a poorly maintained bike), there is a risk of the tool jumping out of the splines if you don’t keep the pressure on. I find that being able to push down with my left hand whilst turning the wrench with my right reduces the likelihood of this.
Once the cassette/freewheel is in your hands, it’s just a matter of getting the culmination of compacted lube and trail dust from the teeth and the spaces in between the sprockets. Bear in mind that if you clean your cassette whenever you clean/relube your chain it will be a much, much easier task. Various companies market long-brushed brushes for getting into sprocket clusters, but I find that a toothbrush/nailbrush and degreaser (Finish Line Citrus is my choice) does the job just fine. Whatever you use, a kettle full of boiling water should be used to rinse away all traces of degreaser before drying the gears thoroughly.
It’s possible, of course, to keep your rear gears in pretty good condition without removing them. The method that I use for cleaning my cassette after a ride is shown below. Although the pictures show the wheel out of the bike, this is only for clarity. This process works extremely well with the wheel still fitted, just make sure the bike is firmly propped up and unable to roll away from you. Of course, you will need to remove the chain.
Only if necessary, I’ll start by applying a small amount of degreaser to an old toothbrush and gently working it around the sprockets. You can hold a cloth directly over your scrubbing action to prevent the unavoidable spray that you’ll create. This’ll keep unwanted fluids away from disc brake components or rim braking surfaces.
My chosen lube (Purple Extreme) and application method means that I don’t usually have much dirt to clean off, but, regardless, here’s how I wipe down the sprockets…
- Now pull down in the reverse action, rotating the cassette on the freehub until you are back to the position you started at.
- Repeat this cycle until the spaces between the sprockets are clean.
- The sprocket teeth can be cleaned by covering a fingertip with your cloth and simply wiping the surfaces clean. This may seem like it’s going to take an eternity, but you’ll find that some teeth require very little effort. If you’ve kept a cassette maintained from new and chosen a clean chain lube, this task is usually fairly swift.
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