2007 C6/A6 Auto Vert. 36k miles

I had the car for 3 months and what I thought was road related vibrations turns out to be drive train related vibration.

This vibration is very strange indeed. It's most distinctive at cruise/55 mph and is a slow cycling vibration felt in the seat and if you place hand on the E brake you can further distinguish the pattern. It comes on and lasts about 2 full seconds and dissipates away slowly for about 2 seconds and come back on cycling over and over.

I've also felt it in the 68mph range, but is only slightly faster in it's cycles. Again, the cycles are so slow that I cannot relate it to any rotating masses of the components of the drivetrain. My only thought is this vibration is emanating from inside the transmission which is a scary and expensive thought.

Anyone experience this?

 

have you looked at your motor mounts? sometimes a side to side vibrations will feel like a rotation vibration

 

No I have not. What would I see? Ya think they'd go bad this soon?


Oh yeah Nice twins. Mine is Automic Orange w/ Beige top

 

Tires are fcuked ...

 

I think the wheels and tires have eliminated themselves by spinning too fast in relation to the slow pulsating cyclical vibration I've described.

 

There are occasional problems with rotating parts which produce a harmonic beat like you describe. I can't tell you if you indeed have tire problems, but it can happen.

Good luck, you'll figure it out and then start enjoying the car.

 

Like Sammy, I can't drive 55 anyway so I don't suffer too much! After managing Super Shops for a few years back in the day, I have felt and trouble-shooted just about every conceivable performance wheel and tire problem. I've never felt anything like this or at least not related to wheels or tires. It's more along the lines of the type of vibration you'd get from loose mounts whether front or rear under hard acceleration, but this comes on at cruise and stays for 2 full seconds and goes away for about the same time. Still does it when you slip it into neutral as well.

In neutral, what is still spinning? 4 tires, 4 wheels, 4 rotors, 8 bearings, 1 driveshaft, 1 torgue converter, 2 halfshafts, and worst of all transmission components, which gives me a haunted feeling in the back of my head.

The transmission theory suggests I test for this vibration in 3rd, 4th and 5th gears in manual mode rather than 6th gear where the car normally cruises. I can imagine the torgue management is in full activation at a mear 55mph in 6th gear.

I still gotta get under the car and investigate all of these possiblities.

 

If you put it in neutral and coast, then the driveshaft should only be turning at idle speed, right?
I think...

Can you borrow a set of good wheels/tires from someone?
Switch out one, then add a second, etc until you have 4 completely different wheels/tires on the car. And keep your fingers crossed.

 

Everything in the car is spinning fast. What you describe sounds like an interference pattern between higher-frequency vibrations. It could well be the tires.

I had the same problem on another car that turned out to be a defective tire. The frequency would increase when I went around curves.

 

The strange vibration that took me forever to find is coming from the air conditioning compressor. Once I pushed the little snowflake button on the ac control it goes away. On a manual you feel it through the clutch. This probably isn't your cause, but is worth a try if you haven't done it.

 

Hmm? That's good idea. At least I could eliminate, or better yet solve the problem rather quickly that way.

 

I have not checked that or noticed whether or not the AC was on, but I'm thinking dropping the rpm to 600 while in neutral would at least change the characterics of the vibration. I guess I could verify this as well.

 

NOW ALL I GOTTA DO IS FIND SOME POOR SUCKER WILLING TO PUT HIS VETTE UP ON BLOCKS SO THAT I DO SOME TESTING WITH HIS WHEELS.

 

torque tube bushings?...you should PM member "RLSebring" and exchange "feelings" with him. He just went through a similiar vibration issue and ultimately discovered a completed wasted torque tube bushing in his 2008 A6 convertible.

 

I assume this is the housing (surrounding the driveshaft) between the engine and transaxle? I'll have to ask your guy about that.

Thx

 

As Ken said I had a pretty good episode with a vibration issue, actually two.

The first cured issue was with my spark plugs. Had a serious engine vibration. Found out my plugs had worn and were at +60 thousants. Put new plugs in and one vibration was gone. Of course I did not know I had 2 at the time.

Second vibration was just manifesting itself. For a long time at WOT I'd get a metallic sound like whipping noise. It grew worst as well as the vibration. I could not quite pin it down whether it was tranny or diff. The bulk of the vibration would start at 3K rpm's and lasted till around 3.5K rpm's then go away. Very strong vibe felt like at the firewall.

It was getting quite worst a few months back st the time we were going to Talladega to run on the track. I had invested so much time into trying to find this vibration that I figured maybe running 150 on the track would isolate the problem real quick. Even with the vibration the car ran great and fast.

Motorhead-47 and Aware02 helped locate the issue of the metallic sound. It was the flex plate vibrating so bad it would hit the starter bendix and throw sparks like a welder.

We were pretty sure the vibration had to be with the torque tube bearings. I bought a low mile torque tube and installed it. Car runs perfect now. The front bearing was totally gone. The only thing keeping the propeller shaft somewhat straight was the drive coupler. It was so bad I ended up scaping the TT.

Sorry about the novel. Yours could be in the early stages or not. My car had + 40K miles when this issue came up. Hope I get more out of this TT.