WORKSHOP TIPS: CLUTCHES

From ZF Aftermarket

Clutch repair is part of the daily schedule in any workshop. Many problems can occur with this wear part, and the causes are not always immediately clear.
ZF Aftermarket has provided the following useful tips on clutches and clutch repair.

Clutch Noise
There are multiple types of clutch noises. Whistling or whining from the clutch can be caused by several factors, such as the release bearing running-off-centre, an off-centre input shaft, or a defective pilot bearing.
On the other hand, rattling noises may be due to load alterations if clutch discs are not furnished with preliminary dampers. These noises do not impair the function or service life of the clutch.
Additional possible causes of clutch noises include the installation of the wrong parts, or installation of the clutch disc in the wrong position.
If a clutch is making noises, consider the following:
• Do the clutch noises occur during setting off or during disengaging?
• Do they occur when the clutch pedal is pressed, while pedalling, or in neutral position?
• Do noises occur when the clutch is engaged, while declutching, or at idle speed?
If the clutch is making noises or whistling, always check the following:
• Is the correct part installed?
• Are all components in the correct installation position?
• Is the pilot bearing installed, and not worn or defective?
• Has the condition of the actuating system been checked?

Clutch Slipping
The problem of slipping clutches is very wide-ranging, with drivers reporting it occurring at different times and in different settings.
For example, it may be reported that the clutch only slips at high speeds. Other drivers may state it occurs when the engine is cold, during starting, when setting off, or in first gear. Perhaps it’s only while accelerating, or after performance tuning.
Clutch slipping systems and causes are just as varied as the symptoms. Even a brand new clutch can be slipping for a variety of reasons. Besides the clutch pressure plate and the clutch disc, clutch slipping causes can often be found in the release system. Additional causes include an incorrectly reworked flywheel or installation of the wrong clutch.
Things to check:
• Wear in release system, freedom of movement, adjustment?
• Are they the correct parts for the vehicle?
• Is the flywheel correctly reworked?
• Is there contamination of the friction surfaces with lubricant?
• Is there deformation and warping of the friction surfaces on the flywheel and pressure plate?

Clutch grabbing
When alternating torques occur in the slip phase (eg. due to friction value fluctuations) and cause vibration of the driveline, this is called clutch grab. Instead of slipping evenly, the clutch grips suddenly, then loses contact. The driver experiences these oscillations as vibrations, rolling or bucking. A grabbing or shuddering clutch produces severe vibration motion and can have various causes.
Why does a clutch grab? In order to know how to stop the clutch grabbing, it is necessary to find out what causes the juddering problem. Apart from the clutch itself, poor engine settings or worn engine or transmission mounts can prevent smooth clutch engagement. Other possible causes for grabbing clutches are installation of the wrong clutch disc or incorrect installation.
Check:
• Are they the correct parts for the vehicle?
• Associated system components/check all parts for wear and correct settings:
– Clutch release system
– Driveline bearings
– Engine management
– Deficiencies in the driveline

Clutch doesn’t disengage
If the clutch no longer disengages, the problem is not necessarily damage to the clutch. Frequent causes as to why the clutch doesn’t disengage correctly can include faults in the release system (clutch release bearing, slave cylinder, clutch lever), a jammed pilot bearing, or non-compliance with important installation requirements.
Check:
• Were all check points observed during installation?
• Are there worn components in the release system?
– Cables, hydraulics, pivot points
– Correct settings?

Sachs Clutches
ZF Services Australia offers clutches, dual-mass flywheels, and clutch actuation systems under its established product brand Sachs, as well as clutch kits that include all the relevant components needed for a clutch repair.

For more detailed information on the full Sachs range and to view more useful Workshop Tips, visit www.zf.com/sachs