Hey all,
I had this posted in the Z06 discussion but I think I may get more help here...

I've been fighting a vibration issue with my c5z for a little while and I'm totally stumped as to what it could be.

A little background on the car.
It has 94k miles
Harmonic balancer replaced with another stock unit at 74k,
Trans rebuilt (sheared 4 gear keys) and torque tube bearings and guibos replaced at 80k,
Clutch replaced at 60 k (vibration existed) by previous owner then replaced again by me at 83k to try and cure vibration (monster lvl2)
And differential mount replaced.

All appeared fine while driving until I started to track the car a little. And found if holding the rpms above 3800-4000rpm (like when going between esses or other steady state throttle conditions) there is a pronounced vibration that gets worse as you keep it at that rpm. When trying to test while stopped, the car will vibrate above this same rpm, and is unaffected by whatever you do with the clutch, whether its in or out, in gear, neutral, the intensity of the vibration doesn't attenuate. It gets a little worse over 4k, and is really only noticable at part throttle, maybe because it doesn't spend too much time at any one rpm when at WOT.

Also of note, I have an LS7 exhaust manifold and X pipe setup, but that was clearanced wherever it needed to be (I hope).

Anyone else had this experience?
I REALLY hope its not the flywheel

 

This is tough because it can be a host of different things, did u check if the original harmonic balancer had weights in it and transfer them to the new one? Also did you hot balance the original clutch with the new monster clutch.
Also what transmission/diff mount did u replace it with?


When I did my first clutch swap on my z06 I damaged the transmission mount causing it to leak, I bought a used oem mount put it in, I had vibrations through out all rpms idle, stopped or moving, it never vibrated originally. Looked all over the web for a new oem mount couldnt find one, so I went with a hoosier torque mount now only I have vibrations over 4k rpm. I also have a stage 2 monster clutch but I never had problems vibrations with that. I think your problem is dependent on the diff mount, the cheap auto parts mounts are crap.

 

Its interesting you say that. The diff mount is a new OEM GM mount I managed to find. I had one of the cheap parts store ones and I quite literally twisted the stud out of the rubber. The one I have is a new one with GM stamped on it. When the cheap mount went, it unleashed a hellish drone on the interior of the car as the trans contacted the subframe.

The clutch/fylwheel/pressure plate was bought as an assembly. And cured a vibration I would have at 1800rpm or so which was for sure an imbalanced rotating assembly.

The harmonic balancer was replaced by a dealer in an emergency, so they took the opportunity to bend me over. I have no idea whether the balancing weights were transferred over, but I DO know they forgot to torque my steering rack bolts!

 

I would suspect the balancer is the culprit if the weights werent checked, also I would go through out the rear drivetrain and check if every bolt is torqued to spec, because a hard vibration tends to loosen up bolts. When I installed my hoosier mount the second time around with the transmission out I used blue loctite on everything.
Yeah the stealership tends to forget to do things right, I also soon have to replace my harmonic balancer also, I have an Ati sitting on my tool chest waiting to be installed once I have time, I would rather do a clutch swap again then have to touch the balancer.