On the left is our new clutch actuator cylinder with release bearingfrom Mid America Motorworks (PN 614-332), with a new clutch pilotbearing (PN 622-779) on the right.
C5 Corvette powertrains were designed remarkably well as a system toreliably handle the performance of a 350-400 hp sports car.
When youpush the envelope much past that, you begin adding extra stress todriveline components, and invariably begin discovering the weakestlinks. In a C5 with a manual gearbox, the component that normally takesthe most abuse (both from the driver and from the engine), and thus isoften the first to go, is the clutch.
When the clutch pedal is pressed,hydraulic fluid is forced into the actuator cylinder mounted to the endof the driveline support assembly, pushing a piston in the actuatorcylinder forward and forcing the release bearing against the center ofthe clutch diaphragm spring to disengage the clutch pressure plate fromthe clutch disc. As the middle of the diaphragm spring is pushed in, aseries of pins near the outside of it cause the spring to pull thepressure plate away from the clutch disc, releasing the clutch from thespinning flywheel. Springs in the clutch plate help isolate thetransmission from the shock of the clutch engaging. When your foot isoff the pedal, the diaphragm spring pushes the pressure plate againstthe clutch disc, which in turn presses against the flywheel. This locksthe engine to the transmission input shaft, causing them to spin at thesame speed. The amount of force the clutch can hold depends on thefriction between the clutch plate and the flywheel, and how much forcethe diaphragm spring puts on the pressure plate.
Before raising the C5 on a lift, John takes out the center console toremove the shifter control assembly from the shifter bracket, mountedatop the driveline torque tube. Also, he loosens the air intake ductfrom the throttle body to prevent damage if the engine rotates laterwhen the torque tube is disengaged.
As soon as we put anintercooled Magna-Charger on Tabula Rossa, our '99 Hardtop, we began tosmoke the stock clutch. It already had 65K miles of wear, and before weeven finished dyno-tuning the supercharged LS1, the massive amounts oflow-rpm torque were enough to overwhelm the friction force the stockclutch was capable of, causing it to begin slipping. In the very firsthard launch we made with the blower (and the only one we dared makebefore replacing the clutch), we smoked the tires and the clutch forabout 100 feet!
We consulted several well-respected Corvette buildersand racers, including Dick Guldstrand (Guldstrand Motorsports inBurbank, California) and Lou Gigliotti (LG Motorsports in Wylie, Texas),who unanimously suggested an Exedy clutch. For overall use as a dailydriver, they recommended an Exedy Hyper Single Disc clutch, which israted for moderately ludicrous performance of up to 500 hp.
Taking theiradvice, we contacted Daikin Clutch, the U.S. subsidiary of Exedy (aJapanese corporation). Based on our current and proposed power figures,the Exedy/Daikin engineers recommended that we step up to a Stage 4 TwinDisc clutch, designed for high-powered, hot street action as well asdrag, road, and rally racing. The twin plate clutches are rated forabove 500 hp to 750 hp, while Exedy offers triple disc clutches for upto and over 1,000 hp. A multi-disc clutch is somewhat heavier, grabbier,and chatters more than a single disc, but it should be nearlyindestructible within our performance goals, even when used hard on roadcourses or drag racing. At a certain point of radical performance, somesacrifices in drivability must be made for durability, and we seem tohave reached that point.
With the Vette secured on a lift and the rear wheels removed, Johnproceeds to unplug the O2 sensors and remove the entire exhaust systemup to the shorty headers. He's already removed the cat-backs, now hedrops out the H-pipe.
Unlike most high-performance aftermarketclutches, which are beefed up and reinforced OEM units, the Exedyclutches are custom-built from scratch. The Exedy Twin Disc clutch, PNGT01SD, is a beautifully machined unit that comes complete with alightweight, chrome-moly steel flywheel, purple anodized forged aluminumclutch cover, and T5001 cerametallic friction materials for extreme heatresistance. We opted to replace the original pilot and throw-out/releasebearings while we were at it, so we ordered a new, OE pilot bearing andclutch actuator cylinder (the only way a new OEM C5 release bearing isavailable) through Mid America Motorworks. These OE replacement partsare available through your local Chevy dealership, but at substantiallyhigher prices. A C5 clutch replacement generally takes approximately 6-8hours because the entire rearend and driveline back of the engine mustbe removed, all of which John Best at West Coast Corvettes took care offor VETTE.
Next, John removes the 36 bolts that secure the driveline tunnelcloseout panel and pulls it away to gain access to the internals. | 
Before proceeding further, John supports the transmission/differentialassembly with a transmission jack | 
The entire rear subframe assembly must be removed, so John unbolts therear shocks, tie rod ends, and hubs from the lower control arms, anddetaches the brake lines from the subframe. Then, with help from hiscolleague, Tito Casio, they unbolt and lower the entire rear sub-frameout of the Vette. |
With the rear subframe removed, John moves a second trans jack in.They've custom-fabricated a support structure that bolts to the C5trans/diff assembly, making the driveline relatively easy to remove atthe proper angle. With this jack attached to the transaxle assembly,John removes the half shafts from the differential, disconnects theclutch actuator cylinder hose, unbolts the driveline support assemblyfrom the engine flywheel housing, and lowers the entire assembly away. | 
Finally, John is able to remove the flywheel inspection cover and beginsto loosen the clutch pressure plate bolts that attach it to theflywheel, rotating the flywheel until all the pressure plate bolts havebeen loosened. Then he works his way around again to remove them. | 
Now John removes the old clutch pressure plate and clutch driven plate(corporate speak for the clutch disc). |