It was a good idea at the time, I assume. Instead of using a spring-centered clutch disk, Porsche engineers decided that using a chunk of rubber would isolate driveline noise and make the driving experience a lot better. Even the automatics used a flex plate that had a chunk of rubber – probably for the same reason.
A while back I read something that said that the 924/944 line wasn’t expected to last very long – they were expendable cars that would be used, abused and thrown away. Here in North America this might actually be true of the 924 2.0L line as the percentage of them still out there running is quite small. However, the 2.0L 924 is still very popular in Europe and especially in the U.K. where the model was built and sold up to 1985. Well, Porsche built a pretty good car and guess what – thirty years later, it turns out that they are not expendable. The rubber clutches have mostly all been replaced by now with the common-design spring-centered Sachs units, and the rubber flex plates for the automatics are pretty expensive as they are pretty rare.
I have found a few cars with an original rubber clutch, changing them when they fail. The rubber breaks apart under the stress of a few decades of work, and the get-me-home safety mechanism kicks in. Our 924S, Sparky, had a rubber clutch disk in it that has served well for 50,000 miles and almost 33 years, and when we recently replaced it, we found that it was actually in pretty good shape.
When a rubber clutch disk breaks, there are three metal tabs in the center that will engage three other metal tabs, allowing the car to move. The driveline clunks around as the metal tabs engage and disengage one another, but it will get you home. This feature is quite interesting and quite novel. And it does work.
Unfortunately there is no way to definitively tell if you have a rubber clutch in your car without taking it apart. That is why keeping records is so important. It’s kinda like the IMS bearing on Boxsters and 996 cars – records can tell the story because you can’t look at something on a lift with a flashlight and see if it has actually been done.
Many 944 owners have never seen a rubber clutch – so the photos are provided. If you get a clunk-clunk-clunk in the driveline in back of the engine, your original rubber clutch disk has probably failed – and its time to replace it.