I decided to write on this subject after hearing many motorcycle owners complain about clutch problems: hard shifts, clutch slip, etc. However, I will exclusively talk about wet-type clutch systems (not dry-type).
Clutch problems are usually the same from one brand to another: slippage, jerky action, hard-to-find dead spot, etc. What you should know is that all these problems are the result of aging (years of abuse). In Canada, most owners only ride 5 to 7 months a year, which leads to chronic clutch freeze. The fiber plates jam due to the pressure applied by the clutch basket spring(s). Their structure loses flexibility and becomes harder, which reduces their grip on metal (or aluminum) plates. As a result, riders can feel slippage under acceleration or at high speed.
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Kawasaki clutch |
In some cases, the springs may collapse. Any spring that remains compressed will weaken over time. Therefore, it is recommended to replace clutch plates and springs as soon as you notice the first of these symptoms. The average lifecycle of a clutch is about 3-4 years. A motorcycle that's ridden all year long will stand a better chance to keep its clutch longer. That being said, mileage and riding conditions also affect clutch durability.
Nowadays, clutches are getting increasingly complex. Most sportbikes and large-displacement motorcycles, like cruisers, feature a rear wheel locking mechanism (also called limited-slip) that can be mechanically or hydraulically controlled. This system is more demanding on clutch plates and possibly requires more maintenance.
When replacing a clutch, you have to pay special attention to the metal plates to make sure they're not warped or faded by overheating. You must replace them as soon as either problem arises. As for fiber plates, you have to measure them one by one or all together by using the method recommended by your manufacturer.
To check if the plates are frozen, wipe them with a solvent designed for mechanical parts and try to scratch the fiber with your nail; if there's no mark, it means the plate is too hard and no longer offers enough grip. The look of the plate is also worth checking: a glazy effect will tell you it's time for a change.