The traditional manual transmission may be decliningin popularity, but for the great majority of enthusiasts attending track days, road races and autocrosses, the old-school stick-and-clutch setup is still the weapon of choice. We may see a day when desire for true manual transmissions in new cars is fueled more by nostalgia than performance numbers, but they aren’t going away any time soon.
And because of that, lots of effort and technology are still being poured into clutch development by high-performance aftermarket companies and OEMs. So before we dive into this special section covering clutches, let’s review a few basics and discuss why a clutch upgrade may be something to consider.
For your car to move, there needs to be a mechanical connection between the engine and the drive wheels. Sounds simple, right? But for your car to not move–which is something cars do occasionally–that connection needs to be momentarily severed. In manual transmission cars, that decoupling is handled by the clutch assembly. In a typical single-disc clutch (we’ll deal with multi-plate clutches in another part of this section) there are two main components: The pressure plate assembly is fixed to the flywheel of the engine, and the friction disc is attached to the input shaft of the transmission.
The friction disc rides on a splined input shaft and is allowed to “float” freely along that shaft. Its travel is constrained by the flywheel on one side and the pressure plate on the other side. When the engine is turning, the flywheel and the pressure plate assembly spin together. When the clutch is fully engaged, the pressure plate presses the friction disc against the flywheel, transferring torque from both the flywheel and the attached pressure plate assembly to the clutch friction disc. This disc is attached to the transmission input shaft, so torque can travel into the transmission and down the line.
When the clutch pedal is depressed to disengage the clutch, the pressure plate lifts off the friction disc, and because the friction disc is allowed to float along the input shaft, neither the flywheel nor the pressure plate assembly can adequately transfer any torque. The pressure plate is lifted from the disc via a diaphragm spring attached to the pressure plate. A diaphragm spring is a disc-shaped spring that lifts its outer circumference when the inner part is depressed. That oversimplifies the importance of the diaphragm spring–lots of clutch operation and feel is dependent on the characteristics of this spring–but that’s the basic mode of operation, regardless of what kind of clutch you’re talking about. But there are lots of variables contained within that basic system. First is friction.
View all comments on the GRM forums
You'll need to log in to post.
