OK, you've graduated from oil and filter changes to tune-ups and even brake jobs. You've got a tool box fairly well-stocked with metric and SAE combination wrenches and sockets, and all the screwdrivers and pliers you'll ever need. You also have the obligatory locking pliers and a BFH or two.
But now you find it tougher and tougher to light up the rear tires on launch, and may even feel a bit of slippage in the clutch. You have a little free play at the top of the pedal, so you believe the clutch is properly adjusted (more on this later), and it's been 40,000, 50,000 or more miles since the clutch was last replaced. Or, more likely, your prized Corvette has seen a number of owners before you, and you have no idea of when, if ever, the clutch was replaced. Suddenly that clammy feeling drifts over you as you have visions of a giant bill to keep your Vette on the road, and you think to yourself, "Geez, is there any way I can do this myself and save some money?"
Good news! You can, and you can, particularly if yours is a C1, C2, or C3. Clutch replacement in these cars is surprisingly straightforward, requiring about as much muscle as it does know-how. To get the low-down, we contacted the folks at S.P.E.C., Inc. who offer a full line of performance clutches and related products. They supplied a clutch kit for our '58 C1 factory 283/270 dual quad car, and also supplied some useful technical information. Here's the deal:
How It Works
A clutch is surprisingly simple in operation. A clutch disc with friction material on both sides is sandwiched between the flywheel and the pressure plate, also referred to as a clutch cover. The clutch disc has a splined center and "floats" fore and aft on the splines of the transmission's input shaft. The pressure plate is bolted rigidly to the flywheel, and has a friction surface that moves fore and aft to clamp the clutch disc firmly to the flywheel when the clutch pedal is released.
A clutch release bearing, also called a throwout bearing, presses against levers (fingers) in the pressure plate which are hinged so that when the pedal is depressed, the bearing pushes against the levers, pulling back the friction surface of the pressure plate. This allows the clutch disc to "float" between the flywheel and the friction surface of the pressure plate so that no power is transmitted to the input shaft of the transmission. The bearing is activated by a pivoted fork and mechanical linkage from the pedal on early cars, and by hydraulics on C4 and newer Corvettes. Simple, right?
A clutch is nearly maintenance-free, save for occasional adjustment and, ultimately, replacement. Since the throwout bearing absorbs rotational energy, it's important that it is separated from the levers of the pressure plate as much as possible. Otherwise it will be spinning constantly and will quickly wear out. A faulty throwout bearing can be readily identified by a whining sound when the clutch pedal is depressed slightly, bringing it in contact with the levers of the pressure plate. This whine tells you that clutch replacement is in your future, since it is labor-intensive to access and replace the bearing and, if the bearing is shot, it makes sense to replace the clutch disc and pressure plate at the same time.
Clutch adjustment is surprisingly simple. A threaded rod with lock nuts is part of the clutch linkage, and the idea is to adjust the linkage to assure that the bearing is withdrawn slightly from the levers of the pressure plate when the pedal is disengaged. Easy rule of thumb—adjust the linkage so you have about an inch of free play at the top of the pedal travel, and so that the clutch starts to engage when the pedal is about a third of the way up from the floor.