Hey guys, I need help!
My 2012 base has developed a shudder/vibration while accelerating and I cannot for the life of me figure out what is causing it. It feels like it is coming from the rear, and it can be felt and heard. it is most noticeable while accelerating medium to hard, If i'm just cruising there are no issues and no noises. Usually only happens in 1st and 2nd, and if there happens to be a dip or a wave in the pavement, it gets worse.
A little back story:
I purchased the car used about 6 months ago. It has higher miles (90k), and I knew it was going to need some maintenance, but did not notice this immediately. The issue seemed to have developed after lowering the car on the stock bolts. The car sat VERY high in my opinion and other cars i've looked at seemed to be a tad lower, so I made some adjustments. The car is not by any means slammed, the front fender height is 26.5" from the ground, and the rear fender heights are 28" from the ground. When i received it, the car sat at 28" front, and 30" rear. I just wanted a modest drop in fender height. I have seen numerous c6's that are absolutely slammed and never read any complaints about noises after lowering. Maybe it's just a coincidence that it began after i lowered, but to me it seems related.
After noticing this vibration the car has had several components replaced in the spirit of preventative maintenance, and in hopes that it would cure my vibration.
Items replaced:
All 4 new tires
OEM clutch and flywheel
OEM slave cylinder/release bearing with the metal retainer insert
OEM driveshaft bearings, and couplers(bmw version)
OEM pilot bearing
RPM stage 2 differential
OEM driveshafts
OEM engine mounts

I do have on order oem trans mounts. They did not arrive in time to replace them with the engine mounts, but so far this shudder/vibration has persisted throughout replacing all of the above components. Am i missing something here? I'm going crazy trying to figure out what's loose/worn but nothing has seemed to make a difference. The above repairs were done in stages. I did the clutch and driveshaft bearings at one time.. This made NO difference, but my release bearing was coming apart, so that did fix one of my issues. The differential was replaced at a separate time due to a noisy pinion. Much quieter ride now, but still shuddering on hard accel. Just this morning I replaced the engine mounts, and rear axles and still with the shuddering. I made sure to follow all repair instructions to the T including torque specs for all fasteners.
Open to any and all suggestions!

Thanks
Brad

 

I forgot to mention this car is a manual 6 speed. I have checked all nuts and bolts on subframe and suspension and everything is tight. has anyone else had an experience like this with their C6?

 

Changing the ride height changed the corner balance and the alignment as well.

Also, since I see a new clutch in the works, did you heat the flywheel up before you installed in on the crank? If no, then flywheel may not be flush/square to crank surface, and where all the vibration is coming from.

Hell, could be that you did not rebuild the torque tube correctly and the vibration coming from there isntead.

 

corner balancing and alignments wont cause this sort of issue
The vibration seemed to occur immediately after lowering and was present before any of the above work was performed.The undercarriage hardware was untouched prior to the aforementioned repairs. All of the above maintenance was done in attempts to freshen up the chassis and hopefully cure my vibration issue. It was present before any of the work was done.

 

Just updating this thread for anyone still around in these boards watching.. finally had time to replace the trans mounts. That would've been so much easier if they had arrived in time to replace while i had the differential out of the car!
Unfortunately this made little to no difference.. The only thing I can think of is that the suspension may be bottoming out on hard accelerations. I'm not hearing any "thud" or hard contact. It's really more of a shudder, but possibly one of the shocks are bottoming out?
My suspension is all stock, but the rear adjusters are lowered all the way. The rubber pads on the bottom of the bolts are intact. Again, the rear fender height is about 28" from the ground, so in my mind that shouldn't be too low? But maybe the stock shocks are running out of travel? The car has FE1 soft ride suspension.
Visual inspection of all components reveals NO rubbing of any kind from wheels/tires to fenders or fender liners and no visible signs of any hard contact being made anywhere..

Edit: ok it's not the suspension bottoming out.. I raised the front and rear back to a higher height closer to stock.. made no difference at all. The vibration seems like it might be RPM related. It seems to be more prominent on hard acceleration, around 4k rpm

 

If at any point you removed the spark plug wires on the spark plugs themselves, double check that each of the are making contact and more importantly make sure none of them are arcing out on a header. A spark plug wire arcing out on a header will cause hesitation like you mentioned. I hope you get if resolved soon!

 

Did not read the OP post closely...
"Vibration... while accelerating... after lowering."

My first thought...bottoming out the rear shocks.

FWIW I'd inspect this work, plus look for damage or loose rear suspension bolts, that's where I'd start.
With the cover/ boot hiding the rear shock shaft/ joust bushing I am not really sure how I would inspect the rear shock travel.

Good luck.

 

Thanks for the tips guys, I appreciate the ideas.. There is certainly not any hesitation although i did check spark plugs and boots and all is well.
Regarding bottoming out of suspension, I lifted the car back up yesterday to stock height and it made no difference.

The more time I am spending with this, the more I'm realizing this vibration seems to be present around 4k rpms. The car is an M6, If i hold it there while in gear i can feel it while driving steady. If the car trans is in neutral or the clutch is pressed, the vibration is still somewhat present but significantly reduced.
Of course it is most prominent on hard acceleration through 4k rpm range and it seems to lessen closer to redline
My first guess would've been something to do with the clutch but it was present before the change, and it still persists after a complete flywheel, clutch and pressure plate change - all OEM components. Also rebuilding the driveshaft with new couplers and bearings made no difference. clutch and driveshaft were rebuilt at the same time.

still scratching my head here.. maybe the driveshaft is out of balance? I made sure to index the front and rear sections of the shaft so i did not get the shaft clocked improperly