Have you ever thought about the myriad complex actions a clutch system performs with one push of a pedal? With a simple movement of your left leg, your Corvette C5/C6’s clutch can help you make a partial or direct connection with the driveline, change gears up or down, creep or rocket away from a dead stop or a roll, and get amazing mileage with far less slippage than an auto trans. Oh, and it can enable power shifts and wicked burnouts, too—but you already knew that. For simply pressing on a pedal, that’s pretty amazing technology.
So amazing, in fact, that clutches are sometimes seen as too complex to understand—people don’t know how they work, as long as they work! But clutches can be actually be easy to comprehend, once you identify the parts involved and have a basic concept of their operation. This article was written to help you achieve that understanding.
First, we’ll cover the components used in clutch systems, as well as the material variations that help separate stock, performance, and race clutches. Next, we’ll review common formulas and calculations used in the design and testing of clutches. We’ll then hear from two of the industry’s clutch experts, who will answer some of the commonly asked Corvette C5/C6 clutch questions.
And finally, we’ll provide the latest aftermarket clutch recommendations for you C5/C6 owners. Whether you’re a granny-shifting cruiser or the kind of speed freak who refers to halfshafts as “fuses,” we’ve got you covered.
The disc is the heart of a clutch system: The attached friction material supplies the friction needed to pass the engine’s torque through the drivetrain. Clutch discs can be a full-face (round) or puck-type design.
Friction materials attached to the middle and outer parts of the disc will affect how the clutch engages. There are several different types:
Organic compounds are usually used for street or street/’strip duty. They engage smoothly, yet can handle heat better than stock clutches. Materials include fiberglass, ceramic, and carbon, although various metals can be added to the blend to increase friction.
Sintered metal compounds are normally formulated for racing applications. A higher friction coefficient means a more positive engagement—they grab harder—but in most cases these compounds are not street friendly. Materials include bronze, copper, iron, and full ceramic.
Exotic compounds such as carbon are more popular than ever, and for good reason: Revolutionary carbon-carbon discs offer smooth engagement, great friction, low weight, and low wear. Once prohibitively expensive for street applications, carbon clutch systems are much more affordable now—and they’re fully rebuildable, too.
At the disc’s center is the hub, which also includes the spline. The disc and hub are connected, but the type of connection determines how smoothly or harshly the clutch engages and disengages. Racing discs are usually riveted to the hubs for solid (but harsh) engagement. Many street discs use hubs with built-in coil springs that allow a small amount of rotation when engaged, which softens the engagement and results in better driveability.
Speaking of driveability, a marcel is a thin, wavy metal plate attached to the clutch disc in some street applications. This wavy plate helps reduce clutch chatter by facilitating a smooth engagement. This plate differs from the ones in racing clutches; as chatter isn’t a concern, they use a flat plate.
The pressure plate actually engages the clutch by clamping the disc against the flywheel. There are several different types:
The ubiquitous diaphragm pressure plate uses many “fingers” that the throwout bearing presses against to disengage the clutch. This type is known for good driveability and pedal effort, and it is found in many late-model vehicles, including Corvettes.
The Borg & Beck is a coil-spring design that uses three levers to engage and disengage the clutch disc; the coil springs apply pressure to the disc. This type was common in classic muscle cars.
Finally, there’s the Long-style pressure plate, which is a Ford version of the Borg & Beck that is used in racing applications.
In addition to standard metals such as ductile iron, pressure plates can also be had in aluminum—they’re lighter, which helps with responsiveness.
SFI-approved pressure plates are the best choice for performance and safety, particularly in cars that see use on the road course or dragstrip.