Clutch replacement questions

I've been driving manual transmissions all my life, with just a five year break for an Audi A4 and a couple of VW TDIs...and then the VW GTI DSG. My manuals included a 57 Chevy, 64 Corvette and many many Fiats and Hondas and Alfas and two vintage race cars and VW Golfs and a Maserati Biturbo and a 308 and my RS America and 993. One vintage race car had a throwout bearing replaced and the 308 had a clutch cable replaced. All the cars were driven hard with the race cars and all the Alfas seeing lots of track time. And when my wheel to wheel days finished, both Porsches made many trips to the Streets of Willow. However I never had to replace a clutch or disc or flywheel on any of these cars. But changing clutches seems to almost be a ritual here on these boards...at least with the watercooled cars. What has been the cause of all these clutch replacements?

Um....not sure where you got that impression. I've read a lot more about people changing out the I*SB and decided to change the clutch the same time while in there.

Just had the oil/filter changed along with a thorough annual "up on the rack" inspection on my 77K mileage '99 996 cabrio. Verdict? The original clutch is now at the end of its adjustability, and I intend to replace it along with the AOS/IMSB/RMS in 2015. I guess I should plan on replacing the clutch about every 75K or so. I don't have a problem with that. 996/997 are not high mntce. cars if regularly driven and properly maintained, IMHO. relinuca

Quotes source post: 11716450

There have been many posts from those suffering(actual or imaginary) the IMSB that have decided to do the clutch simultaneously( and in my opinion, way too soon). I have 69k miles on my clutch and expect to drive many more miles before needing a replacement. So many new owners have decided to be proactive and thus have replaced parts that did not warrant replacement. The answer to your question in many instances is FEAR.

I drove over 120K miles on my 996 before the clutch needed to be replaced.

996's are up to 15 year old cars and many are used as daily drivers. Cars of that age with high miles will need a new clutch eventually. As others have said replacing a clutch while upgrading the IMSB/upgrading the IMSB while replacing the clutch are both very common topics in this forum. It pays to do them both at the same time and my guess is there have been a lot of IMSB's that didn't need to be replaced and a lot of clutches that were replaced before needed as well.

Quotes source post: 11716450

As others have noted often the clutch is replaced when the IMSB (or RMS) is done. Sometimes the clutch is replaced even though it is not really necessary as some owners are really very strong believers of philosophy of while one is there to replace the clutch. IIRC a new friction disc has 1.7mm of disc material -- as measured from the friction surface to the flanged end of the disc rivet. The clutch is considered worn out when this measurement gets to 0.3mm. Clutch disc wear is not linear. A clutch disc with just 0.7mm of disc material left is probably not half worn out, that is halfway to needing replacement, but I do not know what the ratio of remaining life to thickness is. Barring the not too common defective clutch it is how the clutch is used that primarily affects its life. Like you I have never worn out a clutch. Check that. My '89 Tempo developed a slipping clutch and I had to have it replaced at IIRC 18K miles with the car still covered by its 36K miles new car warranty. I argued the clutch was defective and received some goodwill even though the clutch was not covered by the car's warranty because it was a wear item. But I have driven other manual equipped cars and never worn out a clutch. I had a throwout bearing in my '96 Ford Mustang GT fail -- horrible squealing every time I pushed on the clutch pedal -- at around 140K miles but the clutch never slipped. I didn't bother to check the wear but had the clutch replaced. My 02 Boxster's clutch is fine with 285K miles on it. My 03 Turbo's clutch is fine with 125K miles on it. Back when it had just 110K miles on it the tranny came out to replace the RMS. I measured the clutch disc and found it had suffered no measurable wear so I left the clutch hardware alone. The only thing the tech replaced were a couple of small needle bearings that support the pivot lever shaft. I strongly urge owners with manual equipped cars to have the brake/clutch fluid flushed/bled on schedule, every two years. I have found with my Boxster past it change by date clutch fluid can affect the clutch action and even the shifting of my Boxster. It is possible that were I to have ignored this or skimped on this service this might have shortened the clutch (or even transmission) life. (Tip owners do not get a pass. While there is no clutch fluid to be concerned about brake health is very important.)

For me the answer was prior abuse, plain and simple. We went in to do the IMS and found this flywheel and clutch disc staring us in the face! Some hack tried to turn it I believe. This is what we put back in instead!

996's have a weak pressure plate. Always change the flywheel when doing a clutch job on these cars! Do not opt to re-surface/machine it because it'll most likely fail. Ask me how I know...