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Bad clutch? What is this noise?

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I have been having trouble with a clutch issue involving a constant noise from the bell housing area. I have posted here before about this but all previous suggestions have been tried without success. I am attaching an audio recording of the noise, which comes on after the car warms up and is idling in neutral, and goes away when the clutch is depressed. This has been a frustrating process since I have so far spent more than $5000 on trying to fix this issue. The car runs great, but ignoring the noise in the past eventually led to a clutch failure. I have had the clutch kit, flywheel, and throwout bearings fixed about 3 times each by both the dealer and a well-reputed indy. Could this be an issue with the slave cylinder for the clutch? None of this is making any sense.

996 bellhousing noise 1.mp3

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Could the release lever be involved somehow. Maybe bent?

Do you only hear it at idle or is it present at other RPMs. I would guess so.

It might be worth bleeding and then if no success perhaps replacing the slave cylinder, maybe it isn't fully retracting when you release the clutch?

Not sure of your MY but you can get a new slave cylinder for about $110 + shipping.

And then bleeding is fairly straight forward, there is a DIY here on bleeding brakes an slave cylinder.

Edited by logray

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Wow I have never heard anything like that. I hope you get it figured out.. Bent realease lever could be the culprit but I don't know.. Seems odd that your tech can't diagnose the problem.. :eek:

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Thanks for that link. I hope that's not what is truly going on? Can a bad master clutch cylinder produce the noise I describe? Of note, the car continues to perform well with no lag or particularly sticky gear shifts. I'm also able to make the noise go away sometimes when I play with the clutch pedal in neutral.

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Master cylinder noise would be from the front.

Slave cylinder noise would be from above the transmission.

On the rennlist thread speed rII had a good suggestion, can't remember it right now.

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Kind of hard to believe the problem has been looked into 3 times by 2 different shops and no one can diagnose your issue ? I will assume they replaced the shift fork along with the throwout bearing, so beyond that, it sounds like you've got crankshaft bearing issues as one respondent has already suggested as there are no other moving parts where you say the noise is coming from. Time to find another repair shop.

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I guess it may indeed be time to look for some new ideas. Tony Callas at Callas Rennsport was suggested. May be the next stop for me.

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Can you list the components replaced to date?

I would also inspect the crankshaft for movement to rule out a worn thrust brng. Does it make this noise whilst in any gear with any wheel speed or does it increase with wheel speed or engine RPM?

I would also drain the transaxle and inspect the oil for swarf.

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Sounds like your thrust bearing (in engine) is allowing for too much axle play. Have someone start the engine and push the clutch in.... watch the crank pull to see if it moves out when they press the clutch in and moves back in when they release. I dont know the tolerances of the crankshaft axle play but i know its tight. You may even place a screwdriver just in front of the pully, and see if it starts rubbing when your freind pushed the clutch in.

My 2nd quess would be that someone bent (twisted) the clutch fork while doing the clutch job by just pulling the tranny only and not taping the fork down untill the tranny was lined up.

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