How to Bleed a Clutch Master Cylinder
If your car's clutch is not engaging fully or the clutch is slipping, the clutch master cylinder needs to have air bled out of it. You will need a helper to depress the clutch in the car at stages of this operation. Be sure to have extra hydraulic fluid on hand to top up the master cylinder afterward. Follow the steps outlined below to bleed a clutch master cylinder.
Step 1: Find the Clutch Slave Cylinder
The clutch slave cylinder is usually below and to the right of the master cylinder. Find the bleeder valve, a small bolt (8 mm in diameter), that is used to discharge air pressure buildup.
Step 2: Depress the Clutch Pedal and Loosen the Bleeder Valve
Have your assistant step down firmly on the clutch pedal inside the vehicle, holding it down to the floor. Using an 8mm socket wrench, loosen the bleeder valve on the slave cylinder till hydraulic fluid comes out. Have a container handy to catch the fluid. A bubble of air will come out first, followed by a spurt of fluid.
Step 3: Close the Clutch Lubrication System
Tighten the bleeder valve again, and tell your assistant to release pressure on the clutch pedal slowly till it is in its normal rest position. Check the master cylinder to ensure it still has ample fluid. If it drains out and air enters the clutch slave cylinder or clutch hose, you will need to perform the air bleed operation a few more times. Check for any leakage from the cylinders or the clutch hose. If these parts have pinhole leaks, you will need to replace them.
Step 4: Perform the Bleed Cycle Again
Repeat the air-bleeding cycle again, with your assistant pressing the clutch pedal down all the way. Loosen the bleeder valve again and check for more air escaping. Continue to repeat the bleed cycle until only hydraulic fluid drips out of the bleeder valve.
Step 5: Close and Top Up the Clutch Lubrication System
Tighten the bleeder valve for the final time, tell your helper to let off the clutch, and open up the top of the master cylinder to add hydraulic brake fluid till it is topped up. Do not overfill the clutch master cylinder.
Step 6: Clean Up the Area and Put Away Tools
Clean up your workspace of all tools and fluid containers. Wipe off any hydraulic fluid that is on the paintwork and chrome trim, as it can damage painted and chrome surfaces. Clean off your tools of all hydraulic fluid and gunk they may have on them, and put them away.
Step 7: Start the Vehicle and Test the Clutch for Correct Function
Start the vehicle and use the clutch to engage the forward gears. The pedal should feel firm as you press it down, and the gears should change smoothly without slipping or grinding. Test the reverse gear as well for correct engagement.