Describing the flywheel as a disc bolted to the back of the crank doesn’t do it justice. No, this round piece of metal is multi-talented: When the clutch engages and the disc clamps onto it, it’s part of the friction package. It also helps dampen engine harmonics.
Its material determines its weight, which in turn determines its personality: Heavy iron or steel flywheels do a great job of storing engine power, then releasing it to help get a heavy vehicle moving.
Lightweight aluminum flywheels don’t store up much engine power, but they’ll let your engine rev quicker. Aluminum flywheels work best in light vehicles with high numerical gears and/or a good amount of power and torque.
Again, SFI-approved flywheels are the best choice for both performance and safety.
There are three different types of linkages that connect the clutch pedal and the rest of the clutch system: mechanical, hydraulic, and cable-release. They all use clutch-pedal movement to engage and disengage the clutch, but they do it in different ways.
A mechanical linkage uses solid connections—like a pivoting bellcrank and adjustment rod—to push/pull the clutch fork and engage/disengage the clutch. This type of linkage was used in Corvettes through 1981.
A hydraulic linkage uses fluid pressure, a high-pressure hose, and a master cylinder and slave cylinder to engage/disengage the clutch. Because the system uses hydraulics, it doesn’t have a clutch fork. This linkage type is more popular in late-model vehicles, and it was added to Corvettes for the ’84-up model years.
A cable-release linkage uses a simple cable and quadrant setup to push/pull the clutch fork and engage/disengage the clutch.
When a clutch pedal is depressed, a throwout bearing moves the pressure plate away from the clutch disc. When the pedal is let out, the throwout bearing moves the pressure plate toward the clutch disc. The pilot bushing sits in a hole in the rear of the crank, and the front of the trans’ input shaft slides straight into it, keeping it aligned and preventing bearing wear.
Single-Disc vs. Multi-Disc System
Here’s an example of a SPEC puck-type clutch disc. Puck types are known for harder engagem
Single-disc clutch systems, as the name implies, use one disc. This type of clutch reigned for decades, and it had to hold up to some of the most powerful engines ever made. So when clutch builders needed more holding power to live behind those big engines, they simply added more brawn. That meant a larger disc with more friction, and a larger, stiffer pressure plate. It held the power, but it also resulted in much heavier clutch effort—and less-streetable manners.
That all changed when multi-disc systems became available for street cars. Multi-discs are exactly as they sound: Instead of a single disc, these systems use two or even three. There are other differences too: The discs are separated by a thin, O-shaped metal ring called a floater plate. Street applications use a strapped floater plate—the straps connect to the flywheel and “drive” the floater, which reduces rattling when the clutch is pushed in. A stand-driven floater plate secures the floater more positively using bolts and nuts; it is stronger and better for racing, but also more prone to rattle.
There are several advantages to multi-disc clutch systems: When everything else is equal, torque capacity is doubled in a twin-disc kit, and tripled in a triple-disc kit. Pedal effort is substantially lighter—in many applications, a multi-disc clutch pedal is easier to work than the factory single-disc system it replaced. And speaking of light, multiple- disc systems use smaller-diameter discs, which can not only save weight over larger single discs, but improve the clutch’s responsiveness as well.
While they are usually more expensive than a single-disc kit, the multi-disc systems’ high power-holding characteristics and low pedal effort make them a perfect match for today’s high-horse street vehicles. In fact, the fastest, most powerful production Corvette ever—the 638-horse ZR1—runs a dual-disc clutch straight from the factory, and the new C7 Stingray will use a similar configuration when it goes on sale this year.