JMon

While at Roebling Road two weeks ago, I started having an issue with my clutch pedal. When I had to downshift from 5th to 4th going into turn 1 (While braking real hard) I would downshift (While blipping the throttle a little). The clutch pedal was very soft going down (Almost no resistance for ½ half the distance), and would only come up ½ way. (Stuck) Everything felt like it was engaged. I would just stick my foot under the pedal and pop it back up. (I’m real good at that now) It only seemed to happen in that turn during heavy braking. I can drive around normally, and everything feels fine.
The next day, I flushed out the clutch line. (Motul rbf600) thinking that was a heat issue.
The next weekend I went to Road Atlanta.
Same problem right out the door, even when cold. (Turns 6 and 10a).
If I didn’t brake as hard, no issue! Throughout the day I experimented with it a bit, and I kind of see a relationship between how hard I brake and if the pedal is a problem or not. I’ve also noticed that if I don’t pop it back up after it gets stuck, I can still push it down again to disengage the clutch for another shift. Another thing I noticed is while I’m braking real hard, and I keep my foot on the clutch a little, I can feel the clutch go down about ½ way to firm, then I can push it down to disengage the clutch.
Can anyone come up with an explanation for this?

Also, If anyone knows a better place to post this problem, please let me know.

JMon

The dealer is telling me it is a clutch disk. (And not covered under warranty) I don't believe them. It is not consistant with what I think about the problem. I don't know how a clutch disk issue would allow the pedal to sink like that.

Macster

Without knowing anything about the car my first guess would be the brake fluid is old contaminated with a high level of moisture. Hard driving with lots of braking from high speed is causing the brake fluid to boil and while under braking the brake pedal manages to keep its feel but the result in the clutch pedal action loses its feel.

The brake fluid is shared by the clutch hydraulic system, but still not sure of the exact mechanism this can happen, but regardless I believe it is happening.

Absent any other signs of clutch distress, fluid leaks, etc., before I had the clutch replaced I'd treat the car's brake and clutch hydraulic system to a thorough flush and bleed completely removing any and all old brake flud from the brake and clutch lines. I'd go even further, just to be thorough in the extreme and have this done by some shop that can work the ABS to cycle new fluid into the ABS fluid passages and the old fluid out.

Then I'd see how the brakes and clutch behaved under the same circumstances.

Sincerely,

Macster.

MUSSBERGER

Macster is right. Did you ever smell any clutch? If you clutch is toast you would know it. Especially in a 997.

adfsouth

I had the same problem with my car and it drove me absolutely nuts. After very hard braking at the track my clutch pedal would stay half-way down. I could easily replicate on the street by braking hard and kicking on ABS. My dealer tried everything and kept my car for a week. The only thing that solved the problem was to run a crap-load of fluid throught the entire hydrolic system and bleed both the clutch and brakes by hand and by preasure bleeder many times. Somthing must have been contaminated in my fluid and I was using relatively new SRF. Sounds you have a similar issue. Anyway, good luck with it.

Troutman

Had similar episode thus past weekend with my 2006 997. Clutch sticking half way up after threshold breaking and sharp cornering. Bleed my clutch and was still having issues. Jmon, how was your problem fixed?

Ptech1

Have resolved this issue recently for customers by replacing the slave cylinder after several attempts to bleed. Suspect an internal seal issue causing hydraulic vacuum/air pocket able to over power a weaker return spring under heavy loads, and only made worse with high fluid temps or boiling. But, I'm a tech. Not an engineer. Fixed the issue though.

Troutman

Thanks. After reading a few other threads, it seems the slave cylinder is probably the issue. Will get it changed and test it out on a track day in 3 weeks.

hoffarch

Had this same problem after a new clutch including slave cylinder installation. Soft peddle and needed to be returned with foot. Had the system completely re-bled for air in the system. It turned out to be a dying clutch master cylinder.

Troutman

Had a new Clutch Master and Slave Cylinder installed, bleed the lines. Was at NJMP this past weekend with no issues. The old Master and Slave had no signs of leaks.

hoffarch

Installed new master and slave cylinder. Pedal went soft after long one day road trip, then came back slowly next day. Following day attended autocross and soft pedal returned the next morning. Have flushed and bleed system twice. Still not sure what is causing the problem.

Troutman

Sounds like you still might have air/old fluid in the clutch lines. I had bleed my clutch a few times just after the install for my pedal to feel normal.