Clutch slave cylinder and master cylinder replacement on HGVs
The clutch hydraulic system on most modern HGVs operates the same way as on a car: the master cylinder converts pedal movement into hydraulic pressure, which actuates the slave cylinder to disengage the clutch. On HGVs, the components are heavier duty to handle the higher forces involved, but the failure modes are the same.
A failing master cylinder typically shows as a pedal that sinks slowly under steady pressure, or a gradual loss of fluid from the reservoir without any visible external leak. A failing slave cylinder is more likely to show as fluid weeping from the cylinder body itself, or as a pedal that has travel but does not fully disengage the clutch, making gear selection difficult under load.
Before ordering, confirm whether the fault is in the master or slave cylinder. On some HGV applications the concentric slave cylinder is mounted inside the bell housing and requires partial gearbox removal to access. Always flush and replace the hydraulic fluid when replacing either cylinder.
Frequently Asked Questions
How do I tell if the clutch slave cylinder or master cylinder has failed?
A sinking pedal that returns to position when pumped suggests the master cylinder is bypassing internally. Fluid weeping from the slave cylinder body, or a pedal with travel that does not fully disengage the clutch, points to the slave. Physical inspection of both cylinders and the fluid level is the starting point.
Do I need to bleed the clutch after replacing a cylinder?
Yes. Any air introduced into the hydraulic circuit during a cylinder replacement must be bled out before the clutch will operate correctly. On most HGV applications, bleeding is done from the slave cylinder bleed nipple with the master cylinder reservoir topped up. Some vehicles require a pressure bleeder to get a firm pedal.
Can I replace just the seals in a clutch cylinder rather than the whole unit?
Seal kits are available for some applications and can extend the life of a cylinder that has not suffered corrosion damage. On high-mileage HGVs, the cylinder bore is often worn or pitted by the time the seals fail, making a full cylinder replacement more reliable.
Does Truckstop Group stock clutch cylinders for all HGV makes?
We stock clutch slave and master cylinders for DAF, Scania, Volvo, MAN, Mercedes-Benz, Iveco, and Renault. Call us on 01527 598 000 with your chassis number if you need help confirming the correct part.
