C5 Noise in Transmission
Submitted in Corvette Magazine, Issue 100, October 2015, Pages 26 and 28.
Problem: My 2,411 mile 2002 Z06 has the noise and rattle of a throw-out bearing not functioning properly. I contacted GM Customer Service and was told that there are no TSBs or indications of any such problems reported by GM dealers. Yet, an Internet search indicates that multiple Corvette owners have an identical situation.
GM further informed me that they are taking no further action to resolve this issue. Reports of the clutch noise posted by multiple Corvette owners presumably are not considered credible. Is there an explanation for this noise, and perhaps a permanent fix?
Answer: Your car is more than 12 years old, and regardless of the mileage, GM is not responsible for parts that break or wear out at this point. Having said that, what the vast majority of people describe as a rattle from the throw-out bearing in C5 Z06s actually has nothing to do with the bearing; rather, it comes from the transmission’s gears rattling. And difficult though it is to believe, this condition has been described as normal by GM from day one.
All manual-transmission equipped vehicles have a propensity to exhibit gear rattle to one extent or another, but in most cars it is subdued to the point that it’s barely noticeable, if at all. The firing of the engine’s cylinders develop harmonic resonance, and within a certain frequency range, this resonance excites the components in the drivetrain sufficiently to cause gear rattle. Changing the engine’s RPM and/or load enough while driving moves the harmonic resonance away from the range that excites the input shaft, driveshaft and other drivetrain parts, thus temporarily quelling the rattle.
Engineers usually attempt to reduce gear rattle in new vehicles by using sound insulation, vibration dampers in the drivetrain and so on. Other model Corvettes even used a dual-mass flywheel to dampen the harmonics, all but eliminating the rattle. But in an effort to lighten certain ultra-performance models, such as your Z06, a single-mass flywheel was specified. Saving mass is also the primary reason more sound insulation wasn’t used in your Corvette. The gear rattle and its resulting noise will not harm anything or reduce the useful life of your transmission, engine, clutch or any other parts. It may, however, drive you crazy.