In the Clutches of Progress
Not too long after I first acquired my SC I was made aware of the dreaded rubber-centered clutch, one example of which might be lurking between my transmission and engine. I think it was our good friend Eric Steinel who commented, after giving my newly acquired 911 a once-over, “Wonder how long it will be before the clutch explodes?”
This comforting thought stayed with me for several years until I dropped the engine and transmission one winter to replace the clutch (it still worked, but it seemed like a good idea and it was winter and I was bored…). Lo and behold, my SC was not infected with that mechanism. It had a nice spring centered disk that was undoubtedly OEM.
The rubber-centered clutch was fitted to the SC line of 911s for several years of production. The objective was to eliminate some driveline vibration by providing a dampening effect at this critical juncture. Unfortunately, as these clutches aged and were subjected to the heat and stress of the environment between the 3.0 engine and the 915 gearbox the rubber became brittle. When the inevitable failure occurred the bits of rubber would get spread about and could get lodged between the clutch friction surfaces and the pressure plate or the flywheel. Disengagement of the clutch could become impossible.
When the last one was fitted is subject to some conjecture, with owners of ‘83 model year 911s reporting that they have had such clutches removed. What I have recently learned is that the rubber-centered clutch was resurrected by Porsche a few years later. Carrera owners read on.
The ’84, ’85, and ’86 Carreras all used spring-centered clutches. But, when the G50 transmission came along it brought with it a new and stronger clutch of improved design. Though not classified (vilified?) with the SC rubber-centered clutch, this clutch does include a rubber element. Although I have not had one in hand, I am told that it is larger and that the rubber is surrounded with steel that prevents it from doing any mischief, should it become free of its bonds.
Design improvements are always welcome. And the 911 line has seen an extraordinary metamorphosis through its lifetime which has resulted in faster and better cars. But some improvements have a negative side that is often not apparent. Rubber in clutches is one such story. Longevity was lost in the pursuit of smoother and “better”. (Thanks to Walt Fricke and Wil Ferch.)
© W.S. Cline/Rose Lane Garage 2002