National Autoparts explains how to correctly fit concentric slave cylinders.
Best Practice
Prepare the mounting surface
The environment in which the CSC is positioned needs to be totally clean and free of debris. It should locate cleanly and squarely onto the gearbox casing and any rubber face seal or sealant needs to be used in accordance with the manufacturer’s instructions.
Fixing bolts
When located correctly, fit the fixing bolts and torque evenly to 8-12 Nm (dependent upon manufacturer’s specification).
Hydraulic pipe
Traditional threaded design – tighten the locking nut to 10-15 Nm (dependent upon manufacturer’s specification).
Quick clip connecter – release by either pulling or pushing the retaining clip (dependent upon type).
Manual bleeding process
1. Depress clutch pedal
2. Open bleed valve
3. Keep clutch pedal depressed until fluid is visible (don’t release)
4. Close bleed valve
5. Release clutch pedal slowly
Finally, check that the pedal operation is satisfactory.
Potential Problems
Dry squeezing
If the CSC bearing is compressed before fitting, the internal seals become friction damaged as the chamber is not pre-filled with hydraulic fluid.
Cleaning agents and lubricants
Never use cleaning agents or grease on the CSC.
The component is already lubricated and certain products cause a chemical reaction with the seals. The seals (pictured below) are both the same part number but the one on the left has reacted when cleaned with an automotive cleaner.
Over stroking the unit
Don’t pump the pedal rapidly during bleeding. This forces the roller bearing beyond its designed stroke length and the main seal located behind the roller bearing becomes damaged (first picture, below) from fouling the metal end cap at the end of the guide tube (second picture, below).
Pressure bleeding
We do not recommended this method as the unit can be over pressurised, resulting in damaged internal seals.
Incorrect gearbox seating
On most CSCs, the gearbox holds the back plate in place after fitment. If the CSC has not been seated squarely, then hydraulic pressure will eventually force the back plate out of position (pictured).
“National Auto Parts returns analysis shows that the majority of CSC returns were caused by the mechanic not carrying out the correct fitting procedure.”
