Rear sprockets (a cassette or freewheel) collect sand, old lubricant and puddle water. After a winter on the balcony or a few rides on salted roads, orange bloom appears between the teeth, the chain starts to crunch and shifting gets vague.
A quick wipe will not fix it: dirt and rust hide between the sprockets and on the freehub splines. To clean everything properly it is best to take the cassette off. It takes about half an hour and only a few tools.
What you will need
Important: Keep all products away from brake discs, pads and rims. Remove the wheel first and hold it so nothing drips onto the rotor; you can cover the disc with a plastic bag.
Step 1
Remove the rear wheel
Shift onto the smallest front chainring and the smallest rear sprocket, where the chain is slackest. On bikes with rim brakes, open the brake first, then release the quick release or unscrew the thru-axle.
Carefully drop the wheel out of the dropouts and lift the chain off the sprockets.
Step 2
Take off the cassette
Seat the lockring tool fully in the lockring splines. Wrap the chain whip around one of the large sprockets to hold it, then turn the tool anticlockwise with the spanner.
If the lockring is seized, apply WD-40 Specialist Penetrant to its thread before fitting the tool, wait a few minutes and try again. Remove the sprockets and spacers and lay them out in order.
Step 3
Clean off dirt and old lubricant
Apply degreaser to the sprockets and work a brush between the teeth and into the valleys. If you have no degreaser, WD-40 Multi-Use does the job well: it dissolves old grease and grime.
Wipe off the residue with a cloth and warm water and dry the parts thoroughly.
Step 4
Remove the rust
Spray WD-40 Multi-Use generously onto rusty areas and leave it to work for 5-10 minutes. It gets under the bloom and softens it.
Scrub with the brush, using the toothbrush between the teeth. Treat heavy rust a second time. Sprockets eaten away into sharp, hooked teeth are best replaced together with the chain.
Step 5
Refit the cassette and check shifting
Wipe the freehub splines, refit the sprockets and spacers in the same order, lining up the wide spline. Tighten the lockring clockwise with the tool to the torque stated by the manufacturer.
Refit the wheel, put the chain back on and run through every gear. If the chain skips or shifting is imprecise, check the sprocket order and the derailleur adjustment.
Tip: While the cassette is off, check the chain and jockey wheels: if they are rusty too, clean them the same way. A clean cassette with a rusty chain will be dirty again after one ride.
What next
After refitting, give the outer faces of the sprockets a light coat of WD-40 Smart Straw and wipe off the excess, then lubricate the chain with a dedicated chain lube. Do a full cassette clean in spring and autumn, and wipe the sprockets straight after muddy or salted rides.
These uses come from the experience of WD-40 users in many countries. Always follow the instructions and warnings on the product label.
More guides in «How to use».