ZF Services recommends always checking clutch disks for lateral runout before they are installed in the vehicle.
The clutch disk is the component that makes the connection in the center of the clutch. It is a compact, very complicated component which is subjected to heavy loads. Together with the clutch pressure plate, it transfers engine torque to the transmission input shaft. It also reduces the effects of any fluctuation in engine speed on the transmission.
In order to function optimally, new clutch disks must not exceed a maximum lateral runout of 0.5 millimeters. ZF checks each individual clutch disk after production for freedom of movement and only releases the clutch disks for sale which have passed the check: As part of this process, ZF employees lay the clutch disks between two plates which are pressed together with a defined force. The plates are then separated by a certain distance. If the clutch disk is adjusted correctly, it will be able to rotate freely between the plates.
Checking ensures correct operation
In transit to the workshop or to the end customer, there is a risk that clutch disks are damaged during transportation, handling, or storage. Therefore, you must inspect each clutch disk for lateral runout prior to installation - using a special tool in the outer third of the clutch facing. If the measured deviation exceeds 0.5 millimeters, the clutch disk must be corrected using a straightening device. Otherwise the clutch will not disengage properly later on. The tiny gap between the clutch disk and the flywheel or pressure plate is bridged constantly, which results in positive engagement between the engine and the transmission.
Testing: The best alternative
ZF Services points out that a workshop employee takes just three minutes to test the lateral runout. The options for modifying the design of the clutch disks to prevent any damage during transit are severely limited. Ultracompact clutches are not feasible simply because certain functional and weight requirements must be met. ZF Services sees very few alternatives in terms of packaging: A shipping carton, which protects the contents against any eventualities, would make the products far more expensive. Adding a lot more packaging material would be unacceptable from both an economic and environmental standpoint.