Vibration under hard acceleration
 

Maybe some other gear head out there maybe able to help me with this issue. I have and 06 convertible and I have a lot of vibration coming from the drive train under hard acceleration. It started after I had a new clutch put in last year but I just haven’t been able to find it. Yes I would take it back to the guy who installed it, however he has moved his business to another state.

I originally thought maybe the clutch and or fly wheel is out of balance but it only happens under hard acceleration. If I wind it up slowly I don’t get the vibration. So now I am stating to think engine and or transmission mounts. Do these where out often on our cars? Mine has about 40k miles on it and I have been known to push it. I baby it when it comes to maintenance but I do push it at times.

So does any one have any ideas on where I should start looking for the vibration? Has anyone else had this issue?

Might be the torque tube bushings.

I'd start with the engine mounts - they have been known to seperate.

Does it sound like this? http://www.youtube.com/watch?v=LczzhRrwhR4

Mine does this. I don't think the mounts are broke, they're just sloppy.

docbaker,

Where are you feeling the vibration, shifter, seat, floor, etc. ? Is there an rpm that is worse than others? Know this will help with identifing the cause.

I would suggest doing some trouble shooting before replacing anything.

It does sound somthing like this, but worse than what they are getting in the video.

It comes from all those places, shifter vibrates a lot. The sound and the vibration seems to come from under the floor maybe more towards the rear end. It comes on about 3500 rpm but only under hard acceleration if i just creep up the rpm's then it dosen't show up.

From your posting I understand that you feel it while under load, not while under light load. I would suggest running a simple test that can give some clues as to what the problem is.

Step One
With the car stopped, parking brake on, tran in neutral, clutch peddle full out (engaged), slowly rev the engine from idle with your hand on the shifter. See if there is an rpm that the vibration comes in and maybe goes away.

Step Two
Run the same sweep but this time with the clutch peddle pushed in (disengaged). Note if it is the same level of vibration with yourhand on the shifter.

Report back what you find. :cheers:

If it happens under hard acceleration only, I've seen that to be a worn half shaft, pretty cheap and easy to replace.

If you've got access to a lift, buy one and swap it back and forth and see if one of them is bad.

I've been following this thread, because I have that problem too. The difference is that mine is an A6, not an M6.

Now that you've put a possible cause beyond the clutch/transmission, it brings up other questions.

Both the OP's problem and mine started immediately after a removal of the cradle assembly. His for clutch and mine for converter. Neither one of us knowingly had a worn half shaft prior to a change.

Now for the questions.

What alignment concerns upon re-assembly could cause the problem?
Could a worn half shaft now become obvious?
What else could cause the vibration that's related to removal and re-assembly?

For your case, being an A6, if you had the torque converter discounnected from the propshaft that could be the source of your vibration. The flex plate that connects to the converter has three possible positions to bolt up. It's not that hard to pull the access cover and remove the converter to flex plate bolts and rotate 120 degs and bolt it back together and see if it improves. If not, pull the bolts, rotate to the next 120 deg position and try again. In most cases you will find one position that is better than the other two. Be sure to loctite and torque the bolts for the final position. :cheers:

Stupid question.....could it be wheel hop??

Been there, done that. Even tightened the bolts sequentially and torqued in three steps.

Like the OP, I can ease up to 5-6000 in each gear, (1st-3rd) and get no vibration, but do at WOT.

I'm kinda leaning toward the cradle alignment that may have changed the suspension alignment slightly and during WOT when the rear squats it's noticable, but with no squat at lighter throttle it doesn't show up.

I'm mounting new tires tomorrow and will check the alignment a few miles later.

Just to clarify, I wasn’t talking torque sequence. I’m talking about the orientation of the propshaft to torque converter. It has three different orientation it can be bolted up.

Yeah I know. That was the "Been there, done that.", before I added the torque stuff.

I was so lucky that after the 3rd try, I had to rotate one more time to get back to where I started. :rofl:

I've wondered how the factory happens to get it right the first time. They certainly don't go through the same procedure that's in the shop manual. :ack:

I really don't care about the vibration much, as I'm not at WOT a lot.
I'll also be changing the converter again soon. I'm swapping to a higher stall for a couple months during the winter racing season and then back to the 3200 for road trips.

Well, it will be new game again with the new converter. If you wish to play to improve it, you can also take a washer or two and add to one of the bolts. Run the added washers at each bolt location to see if it improves the imbalance. It's a lot easier with and accelerometer and first order analyzer, but in a pinch, trial and error will get you there. :cheers:

fascinating stuff, eric. thanks for the info. :cheers:

:lurk:

I got the same vibration, not motor mounts. Thinking about swapping axles?

try swapping axles. sometimes the CV's become pitted and only give you a problem under acceleration. since it only happens one the side of the CV cup thats driven most (forward), you can actually just swap the left for the right axle and see if the problem goes away. its free but will take a little bit of your time.

Any update on this issue?