A brief guide to diagnosing of drivetrain noise. Words by Iain Treloar and illustrations by Karl Hilzinger.
Cable tension of rear derailleur
Shift to smallest cog at rear (closest to frame), then shift up one gear. If it doesn’t shift, turn the barrel adjuster anti-clockwise until the shift happens fluently.
Derailleur hanger bent
If the jockey wheels in the derailleur are not exactly in line with each other or the derailleur is visibly angled towards the wheel, the derailleur hanger will need straightening or replacement.
Stiff link in the chain
Work your way along the chain, checking that all the links are pivoting smoothly on their pins. If this is not the case, loosen up stiff links with degreaser and then lubricant, pivoting the affecting link back and forth from the pin with your hands.
Chain stretch or cog tooth wear
Use a chain-checker to determine whether the chain has stretched. If it has, or if the teeth on the cassette or chainrings are sharply pointed, replace both chain and cassette (they wear together) and perhaps the chainrings (consult a bike mechanic).
Cassette body or freewheel body is shot
If there is sudden loss of resistance when pedalling forwards, remove the cassette to see whether the cassette body may be badly worn, or if it’s an older style cluster or freewheel (with bearings integrated into cog assembly) the freewheel body could be cactus.
If in lower gear at back, check B-tension screw to ensure there’s ample space to clear the derailleur jockey wheels
The B-tension screw is located at the top of the rear derailleur and determines how far the derailleur sits off the jockey wheels. Winding this in onto the derailleur hanger will push the derailleur down and away from the jockey wheels and stop them rubbing on one another.
If the grinding seems like a vibration felt travelling through the pedals, it may be the bottom bracket.
Check for side-to-side play in the bottom bracket by wiggling the cranks with your hand. Also check that the pedals are firmly secured. If in doubt, talk to a mechanic.
If your drivetrain emits high-pitched squeaks as you pedal, add some chain lube.
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