C5/C6 Clutch Tips from the Experts
For some insight into ’97-up Corvette clutches, we picked the brains of two experts in the Corvette clutch market: Bob Scheid of McLeod and David Norton of SPEC. Here’s what they had to say:
VETTE magazine: How much torque can a stock Corvette clutch handle?
SPEC’s David Norton: The last new stock C5 clutch we had tested at 436 foot-pounds. That is right at breakaway, so the wear rate would be very high.
McLeod’s Bob Scheid: They were designed to hold the factory power during street use. If you exceed that power level or use it at the track, then you run the risk of clutch failure.
Most clutches will give you indicators that you are overtaxing them: Getting that dreaded clutch smell is a sure sign; so is a change in the pedal position when the clutch engages. An overheated stock disc glazes, and a worn disc thins out. When either one happens, the clutch will no longer hold the power it used to, and it may start to slip.
C5s and C6s are different from most other cars in one aspect: Their pressure plates are diaphragm-style units like most modern cars, but when pushed to high rpm, that diaphragm can get sucked in and cause shifting problems.
VM: What are the C5/C6 clutch’s weak points?
Norton: The ratcheting mechanism is the C5/C6 clutch’s weakness. There are too many parts [that can] fail, and they hinder high-rpm actuation. The units are fairly low in load, but not terribly low. The C5 units didn’t have enough feedback to assist the hydraulic system in returning the pedal.
The flywheel is the worst part of the C5 system: The castings were bad, so there were porosity issues that caused pits and warpage—and they weren’t meant to be resurfaced. They also weren’t balanced separately of the stock clutch, so balance issues existed when end users tried to reuse them without extra balancing steps.
Scheid: The factory clutch’s pressure plate and disc material were built for stock power levels, not for the power that most modified C5s and C6s are making.
VM:What important things should customers understand when choosing a clutch?
Norton: Inertia properties are commonly misunderstood. The benefits of lighter parts normally far outweigh any downsides. The trick is gathering enough info from the end user about their build, and how the car is driven, to determine how light the unit can be to optimize performance.
Scheid: That a higher “Stage” number doesn’t necessarily mean that it’s a better clutch for you. The clutch material, pedal pressure, and other design factors are what’s really important.
For street-driven vehicles, a clutch that has a high amount of holding power, yet uses a friendly disc material and has a soft pedal effort, is ideal.
Also, clutch weight affects both performance and driveability. A lower-weight unit will get more of the engine’s horsepower to the wheels, since less power is being used to rotate the flywheel and clutch. The tradeoff is that you can sacrifice some driveability if the weight is reduced too much.
VM: What should C5/C6 owners’ main considerations be when changing the stock clutch?
Norton: The normal considerations apply, like making sure the capacity covers the modification level, [as well as] driveability preferences and budget. Everyone may prioritize those considerations differently.
And they should always change the stock flywheel. The original C5 flywheels were not meant to be reused, and the stock cast units were not balanced independently from the factory. The C6 flywheels were better, but the stepped design limits performance and reliability to the self-ratcheting stock clutch design.
Scheid: The three most common concerns are holding power, driveability, and clutch life. Quality is always priority one when designing our clutches, so we must be able to supply the customer with a high-quality clutch that meets those three needs.
Clutch life has a lot to do with the way the unit is used. Of course, a clutch that is used for racing or abused on the street will not last as long. Customers will get long life out of our clutches if they choose the proper clutch for the way they are going to be using it.