How many miles did the rubber-centered clutches typically last before disaster struck? I've run across a few 911s in my search and some owners don't know (2nd or 3rd owners) if the clutch was ever changed.

 

this is from "the used 911 story"by Peter Zimmermann...
Average life, from our experience, is only about 25,000 miles, while more than a few clutches have we have repaired are well past 60,000 miles with no need of replacement.

 

I would approach these cars with the assumption that they still have the rubber centered clutch & use it as a negotion tool if you otherwise like the car.
Good for $750-$1000 downward negotion

 

I got 87,000 miles out of mine. However, when it went south, the rubber crumbled and I couldn't depress the clutch while the motor was running. If I killed the motor and put it in gear and released the clutch it would move, but the centrifugal force of the flywheel would throw the crumbled rubber such that after I started it, the pressure plate couldn' be depressed. That was nerve racking for a couple of hours out in the middle of nowhere. I had to drive several miles in 2nd gear.

 

Is there any way to tell if it has been changed?
Other than receipts?

 

you need to differentiate the nasty SC rubber centered clutches from the later ones. The 1978-83 SC series used the rubber-centered clutches with a large amount of rotational twist allowed...these were the puppies that failed so miserably. The following 3.2 Carrera series with 915 transmissions ( 1984-86) used spring centered clutches ( as did very production SC's)...but Porsche went back to rubber -centered for the 87-89 3.2 Carrera's using G50 transmissions. These later style only allowed a small rotation and had mechanical limit stops built -in. although they can fail like the earlier versions, I woiuld be much less concerned over this type compared to the originals.
---Wil Ferch