Bleeding or evacuating air from a sealed clutch system is a simple process. Whenever air is trapped within a hydraulic system using fluid as the core medium, a condition called pressure compressibility can occur.
At a practical level, experiencing air within a clutch system usually causes low pedal throws and ineffective gear engage/disengagement. For the driver there are three approaches to resolving this situation:
- Manual process – In this case one person pumps the clutch pedal while a second person opens and closes the clutch bleed valve
- Pressure process – In this event, the system can be pressurized using a stand-alone pressure mechanism, thereby ‘pushing’ hydraulic fluid in/out of the clutch master cylinder as the clutch bleed valve opened/closed
- Vacuum process – In this situation a secondary vacuum system is used to ‘pull’ fluid from the clutch master cylinder and consequently draws and traps both fluid and air into an adjacent stand-alone vessel
In all cases, it is important to use the proper bleed sequence to ensure that air is entirely removed from the clutch system. This information is typically described in each auto owner manual, or via a particular brand service manual.