1991 ZR-1 Vette had new flywheel, Dual clutch disc and pressure plate with new hydraulic throw out bearing installed, now the car rattles like marbles bouncing around in the bell housing.  It gets very loud when the car is idling in neutral and when you leave in 1st gear.  This was done by a corvette shop and I was told that this is normal for that car.  It rattles so loud it sounds like someone is hitting it with a hammer.  Any suggestions on what happened?

William

The ZF units DO have a high degree of "gear roll-over" at idle that can get loud. It's a by-product of the clearance between the gear teeth, and the engine pulses that create a noise. The dual-mass flywheels were developed to combat the noise, and they DO help make it quieter, but they do not eliminate the source of the noise. I would guess that the shop either screwed up the install, changed the dual-mass flywheel to a solid flywheel with solid center discs meant for a dual mass(a definite noise maker), or something along that line, assuming the noise was not as loud before.

I would be very surprised if the flywheel was replaced with a dual mass unit. I had to do mine a number of years ago and it was hard to find. I have followed things along since and basically they are no longer available. Your shop should be able to tell you exactly what they did. I do note that some suppliers are providing single mass upgrades that apparently do not cause excessive noise.

William, I know that your post was dated a few years ago. Just wondering if you were able to resolve the rattling issue ? I have a 1990 ZR-1 with the same irritating issue. Car has 35,000 miles with all original flywheel, clutch, pressure plate etc... The infamous Bill Boudreau ( ZF DOC ), had the tranny out last June. He replaced the input shaft bearing " only "; never replaced the rear main seal, clutch assembly or the flywheel. I know that Carolina Clutch makes a single mass flywheel / clutch / pressure plate assembly that has to be pre-balanced before installation. Don't know if that would cure the so-called " gear rollover " noise ???    Thanks for any reply, if you're still on this forum.  John V.

Although this is a reply five years from your post. I had never heard of this problem before. I haven’t had this experience with mine. The first person that comes to my mind to ask is Mr Haibeck http://www.zr1specialist.com 

He’s been extremely helpful to me and has with other people as well.