Flywheel wear can affect starting behaviour and cause jerky clutch engagement, even after the clutch has been replaced. Although the flywheel is extremely durable and therefore not included in the usual clutch spare parts kits, even this massive component is subject to wear and tear over time.
The friction surface, for example, has a conicity that is barely visible to the naked eye. It is tapered by a few tenths of a millimetre so that the friction disc does not abruptly apply, but instead makes the start-up process as smooth as possible. However, this taper can wear out through after long use. If this happens, the frictional connection is established without transition when the clutch is engaged, which leads to the problems described above.
Incidentally, this jerky behaviour is not only a comfort disadvantage, but can also result in driveline damage.
Another point on the flywheel that is subject to wear is the starter ring gear. The engine is likely to be started several thousand times during its service life, meaning that the starter pinion meshes with the ring gear correspondingly frequently, wearing away the material. This can result in starting problems. Other criteria for assessing the condition of a single-mass flywheel are local thermal overloads or cracks in the contact surface.
The aftermarket division of ZF recommend that commercial vehicle workshops intensively inspect the vehicle's flywheel every time the clutch is changed. It is recommended that the customer replace it at an early stage or at the same time as the clutch if there are any signs of wear. Replacing the component does not incur high additional costs, but can prevent expensive consequential damage.
ZF Aftermarket’s Sachs brand is said to offer an extensive product range of flywheels for trucks and buses from virtually all well-known vehicle manufacturers.