Air keeps getting into clutch line?

[Andrew Howell]

Hello,

 

I have a 2001 Boxster S with the 6-speed transmission and I've been having issues with the clutch for a while now.  I first had an issue about a year ago where the clutch pedal would stick to the floor but only after a few laps at the track or if it was really hot outside.  Not long after that happened a few times, I heard a loud snap/ping noise that came from the back of the car when I pushed the clutch pedal in and the clutch pedal became much easier to depress, but the car still shifted and everything seemed to work.  I suspected that the pressure plate had cracked and when the clutch pedal began to stick again a few months later, I just assumed it was all related to the failing pressure plate.

 

About 2 months ago, I pulled the trigger and dropped the transmission to find a big crack in the pressure plate.  I ended up replacing a bunch of stuff while I was in there, including clutch, pressure plate, slave cylinder, IMS, timing chain tensioners, and a lot more smaller stuff.  After getting the car back together, it drove great and I put over 500 street miles on the new clutch without any issues.  A few weeks ago I took the car to an autox with the PCA and the car performed great throughout the day and gave me absolutely zero issues. 

 

Then, maybe a day or two later, the clutch pedal started sticking again, but this time the pedal was sticking about half way through its return travel instead of sticking near or at the floor.  After driving it a few more days, I had an experience where the car didn't want to go into gear with the clutch fully depressed and it took a few tries to get the car into gear.  The pedal also felt spongy like it had air in the system again.  I checked the bleed screw and all connection points but I never saw any signs of a leak. 

 

Since I had already replaced the slave cylinder, I decided to go ahead and replace the master cylinder as well so I did that about a week ago.  I have a power bleeder so I bled the system thoroughly and the pedal felt good while the car was on jack stands so I cleaned up and dropped the car for a test drive.  When i started the car and went to back out, the car didn't want to go into reverse, or any other gear.  The pedal was spongy and it again felt like there was air in the system.  So i put the car back on jack stands, hooked up the power bleeder again, and pushed another quart or two of fluid through it.  Again, it felt good while the car was in the air, but when I dropped the car and went to take it for a drive, the pedal was spongy and it wouldn't shift into gear.

 

I have heard about the metal coil in the clutch line developing leaks, and I have inspected this part very closely but I do not see any fluid leaks near the coil or anywhere else along the clutch line that I can see.  If there is a leak in the line somewhere, why can't i see any fluid leaking out?  Could there be a pinhole leak that is so small, it only lets air in but not fluid out?  Is that even possible?  I'm considering replacing that section of line anyway but if I'd prefer and not spend $300 on a small hose if I can avoid it.  I've spent enough on this car in the last few months!

 

Some other symptoms I noticed this weekend are, the clutch is making a loud squeak from inside the bellhousing when I push the clutch in and out.  Also, with the clutch pedal fully released, I can sometimes hear a noise that sounds like flywheel rubbing up against the clutch disc.  Is this simply because air in the line isn't allowing the clutch to fully release?  Or is there any possibility that something is wrong with the clutch assembly?  I'm fearing that I might have to drop the transmission again if the flywheel is backing out or if there's an issue with the TOB or something else.  Any ideas or thoughts would be much appreciated!

[Loren]

Have checked your clutch pedal and boost spring to see that it is working correctly?

Are you using a pressure bleeder (under 20 PSI)?

 

[Andrew Howell]

Hi Loren, thanks for the response.

 

I removed the boost spring a few weeks ago to inspect it and take it out of the equation.  The spring and housing both seem fine so I don't think it is spring assist.  I've left it out of the car for now.

 

The pedal appears to be functioning correctly but I can't be 100% sure.  Between replacing the master cylinder and removing the spring-assist, I haven't noticed anything out of the ordinary.  Is there another point of failure that I should be looking for in the pedal mechanism?  

 

Yes, I'm using a pressure bleeder and keeping it between 15-20 PSI.  I've put at least 3 quarts through the system now after 4-5 bleeding attempts.  I had a friend stop by to activate the clutch pedal by hand while I was adjusting the bleed screw just to be extra thorough but I keep having the same issue.  

 

The last time I even started the car while it was still on jack stands and everything seemed to work fine immediately after bleeding.  I could shift through the gears and let the clutch in and out without any issues and it felt fine.  But then 15 minutes later, after cleaning up and getting the car back on the ground, the clutch pedal felt spongy and it wouldn't shift into gear again.  If I pump the pedal i can get it into gear but then the car starts moving before I lift my foot off the clutch, especially if i rev the engine.

 

It really feels like air in the system but don't see any signs of fluid leaking anywhere.  Any other thoughts?  Does replacing that line seem like a good, logical next step?

[Loren]

If course you know that the clutch slave and the brakes share the same reservoir. So a leak in one may affect the other.

[Loren]

Are you using this procedure to bleed the clutch?

 

Optional Clutch Bleeding
This is best done when you are bleeding the left (driver's side) rear wheel as the clutch bleed valve is mounted high above the axle on the transmission.

1. Push the clutch pedal in by hand (very slowly) and use a long piece of wood to hold the pedal down. I wedged the other end (of the wood) between the seat and door frame -- with plenty of soft padding to avoid scratches. A second option is to have a 2nd person sit in the car and keep the clutch pedal FULLY depressed.
2. Open the clutch bleeder valve until clear, bubble free brake fluid emerges (at least 30 seconds according to Porsche). Remove the wood. Then, pump the pedal again very slowly by hand for a further 60 seconds. After pressing the pedal down fully about 10 to 15 times, leave the pedal in its normal position. After allowing a fill time of 90 seconds, check that no more air bubbles appear at the bleeder valve (use a collecting bottle with a transparent hose). Then close the bleeder valve. Wipe off the area and replace the rubber protective cap over the bleed screw.
3. You may notice that the clutch pedal does not return... so carefully pull it up (slowly) to it's normal position. Then depress it (slowly) a few (at least 5) times. In a few cycles the feel should return.

[Andrew Howell]

Yes, that is the procedure I have done maybe 4-5 times now and yes, I do see how everything connects back to the brake fluid reservoir.  Everything will feel great immediately after the bleeding process but by the time I try to drive the car (maybe 10-20 minutes later), the pedal will feel spongy and it won't go into gear.  If I jack the car up again and do the same process I get the same results, at least that's how its been for 4-5 bleed cycles now.  I've read that other people have struggled to get air out when replacing the master cylinder but I have a hard time believing there's still an air pocket somewhere with the pressure bleeder and all the fluid I've bled through it.  Plus I was having similar symptoms before I replaced the MC and i cut open the old MC to inspect the seals and everything seemed fine, I don't think there was ever a problem with the MC.

 

The more I'm thinking about it, the more I'm suspecting a small/pin hole leak in that coiled hard line that connects to the slave cylinder but I'd like to have a bit more evidence before I order a replacement line.  It really seems like air is being introduced to the system somewhere.  I have replaced both the master and slave cylinders so I have been going over all the connection points but nothing appears/feels loose and I don't see any fluid leaks anywhere.  Why don't I see any leaks?  Maybe the new slave cylinder failed after the autox?  I was worried that I might have striped the bleed screw or the input line to the SC but again, I don't see any fluid leaking out even with 20 PSI on the power bleeder.  

 

I apologize for the long posts but I'm paranoid that I made a mistake with all the work I've done recently and I wanted to get some of my concerns written down incase someone else sees a red flag.  I really appreciate your input, Loren!