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Bleed clutch master and slave using vacuum

On the first track day with the Z06, the clutch pedal stuck to the floor as I shifted at high RPM. Imagine my surprise and disappointment. I could pull the clutch pedal up and continue, but it would repeat itself at intervals. I tried the "ranger method" numerous times to bleed the slave cylinder, but it didn't help. 

I was about to start pulling down the exhaust etc. to access the bleed screw and purchase a Tick Master Cylinder, but then I found this thread: Clutch bleeding from the mc

I figured I should give it a try:

I drained and cleaned the reservoir and refilled it with new high temp brake fluid (Castrol React Performance DOT 4). I then applied vacuum to the master cylinder port using a Mityvac. As can be seen, a lot of air pockets and old fluid was released. The vacuum makes the slave cylinder collapse, which squeeze out more of the old fluid than when using the ranger method. New fluid is sucked in by the reminding vacuum when the MityVac hose is removed. I repeated this process until only clear fluid entered the bottle.

The slave cylinder then has to be "uncompressed" by pushing the clutch pedal a few times. This will draw in additional brake fluid, so watch the reservoir level.

In addition to bleeding the master and slave cylinder, I also

  • removed the clutch pedal assist spring
    • This has the additional bonus of removing the artificial feel of the clutch pedal. First half of the pedal travel it works against you, then the geometry changes and it helps you to push the pedal downwards. This ruins the linearity of the clutch
  • added heat insulation to the clutch line
  • moved the clutch line further away from the exhaust manifold
  • drilled holes in the bellhousing rear plastic covers, to allow hot air inside the bellhousing cavity to escape.
Update September 2023: The above actions made the clutch work satisfyingly for another 3 years (until it was time to pull the drivetrain to repair a broken rear differential)!
The reason for the poor performance of the slave cylinder clearly became visible as I removed it at 110k miles, while installing a new Lightweight clutch kit