Ducati MONSTER 821 Workshop Manual page 1015

excessive wear of the hub or clutch housing.
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A clutch which slips may be caused by:
no backlash of the control lever;
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worn clutch plates;
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weakened springs;
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faulty clutch release mechanism;
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excessive wear of the hub or clutch housing.
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A noisy clutch may be caused by:
excessive backlash between the primary drive gears;
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damaged primary drive gear teeth;
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excessive housing between driving plate tabs and the clutch housing;
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worn gear/clutch housing bearings;
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the presence of metal particles (filings) on the gear teeth.
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