You Too Can Perform Under Pressure.
Obviously, a whole lot more clamping pressure is needed with this much annihilating abuse on the clutch mechanism. But most performance car owners would prefer to keep the pedal pressure light so their left thigh doesn't ache after tooling around town in stop-and-go traffic.
Explaining how to increase clamping pressure while reducing pedal pressure first requires covering a couple of basics. As any experienced service pro already knows, most original equipment clutches are diaphragm clutches. The two primary components of the clutch are the pressure plate and the clutch disc. The pressure plate has to apply and maintain just enough clamping pressure to the disc so the engine torque reaches the driveline.Since the clutch components are already spinning, Centerforce installed a system that takes advantage of this centrifugal force by adding weights to the fingers of the pressure plate. As the engine revs increase, the weights move out, applying higher clamping force against the pressure plate and causing lockup at a faster, smoother rate. The faster and smoother the shift, the less friction is generated, so there's less heat that could result in clutch fade and slipping.
Centerforce's clutches come in a variety of levels, but on a performance machine, like the supercharged 2000 Corvette C5 project car shown here, the company recommends its Dual Friction clutch, designed specifically for high-horsepower, high-torque applications that generate near flash-point heat. The Dual Friction disc uses a specially formulated thermal resin compound on one side to maintain strong performance at those higher temperatures. The opposite side is a non-asbestos disc facing for maximum capabilities at lower temperatures and smooth engagement. The Centerforce Dual Friction disc has a full facing on the pressure plate side for drivability and longevity, while a carbon composite puck-style (segmented) facing is used on the flywheel side for a positive engagement and increased holding capacity.Drawing from Centerforce's "Clutch Bible," we gleaned a few other recommendations when replacing the clutch.
- Use only factory recommended fluids in transmission and clutch release hydraulic systems to ensure proper release and maximum life of the clutch components. (Some aftermarket synthetic transmission fluids might not provide the necessary friction levels.)
- Be sure to check the bell housing and/or engine block dowel pins for wear. Using all proper dowel pins helps ensure proper bell housing alignment, including parallelism and concentricity.
- Always resurface or replace the flywheel prior to installing a new clutch disc and pressure plate assembly. This ensures the clutch disc friction material seats into the flywheel properly.
- Check the clutch disc on the transmission input shaft before installing onto flywheel to ensure fitment. Often clutch chatter, vibrations or premature wear are not related to the clutch disc and pressure plate. Instead, other problems (misalignment, flywheel resurfacing, pedal/freeplay adjustment and run-out) are responsible for the majority of clutch failures, premature wear or poor performance.
- On the C5 shown, you'll need to bleed the brakes and then make sure the clutch hydraulics work properly. You should not have to bleed the clutch hydraulics because it has the dry connection.
- If everything operates and engages smoothly, take the car out for a spin. Follow the proper break-in procedure to prevent damage to the clutch assembly.
Steve Temple is a freelance technical writer and photographer with more than 25 years' experience. He has served as director of sales and marketing for Shelby American and as online editor for magazines such as Hot Rod, Car Craft and Rod & Custom.