So I had a Monster LT1-S clutch installed in my GXP this week. Mods are in sig. I picked this clutch because EVERYONE says it drives like stock but has more holding power. The only negatives I've ever read about the clutch were related to slightly increased gear rollover noise. Monster's website and everything I've read on the G8 forums and Corvette forum say the car will "drive factory smooth." So naturally that is my expectation.

I'm not close to the car right now, so my dad dropped it off and picked it up. I have not had a chance to drive it yet, and probably won't for a long time. So the issues I describe below are as they were described to me.

Dad picks it up Thursday. He is impressed with the pedal feel and describes it as similar effort to stock, but a much better feel because of the engagement point. He describes no chatter whatsoever, so sounding good so far. However, on the drive home, he said at about 75 mph and around 2000 rpms he got a vibration that shook the car enough to make the rearview mirror unusable. Turned right around and took it back to the shop. Shop tech could duplicate it on the subsequent drive around, but shop manager says its a harmonic in the car that has been become more noticeable because the LT1-S clutch doesn't have the dampening springs that the factory clutch disk has.

So I correspond with the manager over email, and he insists it is a harmonic that is "worse on your car due to the exhaust note/tone and the fact that it's relatively stock otherwise." I ask if they balanced the flywheel and pressure plate, and he said they did. He does not appear interested in re-balancing, and said that if it was out-of-balance, it would vibrate even at idle. Also said the reason Corvettes don't have the issue is because the torque tube absorbs the harmonics. I've actually read the exact opposite on Corvetteforum where the torque tube makes the harmonics worse and makes match-balancing that much more important on a Corvette than "normal" cars where the trans is mated directly to the engine. Also read one C5 owner that installed an LT1-S and had vibration in a certain RPM range until it was re-balanced/match-balanced.

The only solution the shop manager has for me is to go back to stock. And so far I get a very "take it or leave it" attitude from the shop. Just looking for opinions here from those with an LT1-S in their cars. I have never heard any of you speak of a harmonic induced by this clutch, let alone one that occurs at an RPM range that the car will cruise in a lot of the time. I've got my dad driving it a bit more to narrow down all the combinations that cause the vibration/harmonic, but so far, it does not sound like this clutch "drives factory smooth."

Sorry for the book, but thanks for any insight.