S.P.E.C. Inc. supplies clutch kits for street, racing and off-road use. Their clutch kits include all the parts needed for a clutch job—all-new disc, pressure plate, release bearing, pilot bearing/bushing, and clutch alignment tool and, unlike rebuilt clutches, do not require return of the old clutch core. And, happily, all their clutches are machined and assembled in the good ol' U.S. of A.
Diagnosing Clutch Problems
Typically what goes wrong is that the friction material on one or both sides of the clutch disc simply wears out from use, just like brake pads or shoes wear out. The most common symptom of a worn-out clutch is slippage, especially when launching or hard up-shifting. The easiest way to verify this is to set the parking brake, carefully(!) give the engine some gas while holding the brake pedal firmly, and letting the clutch pedal out slowly with the transmission in fourth gear, where it transmits the least torque. If you can't stall the engine with the car stationary, and/or you can release the pedal entirely with the engine still running, you've got a clutch job in your future. Likewise, if you have the throwout bearing noise described above, you're looking at a two-night job with a hefty friend or two.
Less common is fatigue in the spring action within the pressure plate that leads to slippage or total clutch failure, but the result is the same. And, of course, if you install a brand new quality clutch like one from S.P.E.C., such a failure is highly unlikely.
Time To R&R
Clutch replacement in early cars is not too difficult, even if you've never tried something this involved before. Basically, the job involves removing the transmission and the clutch housing, also called the bell housing since it's kinda bell-shaped, unbolting the clutch assembly, installing a new clutch and reinstalling the tranny. Of course you'll need to remove a couple of other items first, including the drive shaft, the shifter, the speedometer cable, and disconnect the clutch linkage. You'll also have to support the engine in order to remove the transmission cross member, which also serves as the rear engine mount. But that's not as tough as is sounds.
Just like you have brake drums or rotors turned to restore a like-new friction surface, the folks at S.P.E.C. strongly recommend that you have your flywheel resurfaced during clutch replacement in order to provide a fresh, proper friction surface for smooth, reliable clutch action. And you'll also want to replace the pilot bearing which, on early Corvettes, is actually a bronze-like bushing that's pressed into the back of the engine's crankshaft to provide a support for the front of the transmission input shaft.
There are really just a couple of cautions when doing this job. The most notable is assuring that the new clutch disc is perfectly centered with the pilot bearing/bushing, since you'll be lifting a heavy transmission up and sliding the input shaft through the splines of the new clutch disc and into the pilot bushing. The tricky part is not in getting the splines to line up, but rather getting that last inch or so of travel as the nose of the transmission input shaft enters the pilot bearing/bushing. It is an absolute no-no to allow the transmission to hang on the splines of the clutch disc without the input shaft firmly planted in the pilot bearing/bushing. Otherwise you will almost certainly bend and warp your nice new clutch disc and suffer poor clutch performance and premature wear. S.P.E.C. includes a clutch alignment tool in their kits to ease installation and prevent damage to your new hooker-upper. Remember, there's never enough time to do it right, but always enough time to do it over again! So do it right the first time.
The following photos illustrate the procedure for changing a clutch in a C1. The process is similar for newer Corvettes, although you'll be working in closer quarters on the '63-up models and, therefore, there's less working room and you'll need a bit more time and patience. But the individual steps are pretty much the same. Starting with the C5 Vette, these cars used a "torque tube" to connect the bell housing to the rear-mounted transaxle (transmission/differential), and so clutch replacement on these cars becomes more involved and may be best left to a specialty shop or experienced friend. And, finally, we strongly recommend that you put the squeeze on your favorite friend with a lift, since clutch replacement is possible, but challenging, if done on the floor.