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Discussion Starter · #1 ·
Just thought that I'd post this information in case it helps someone else. It does not seem to be a common issue, which is why I'm posting it (have never heard of anyone else having the issue and even the GM dealer had to call GM for "help" with this one).

The Car:
- 2012 Impala LT w/19k miles.

The problem:
- I kept hearing a "clunk" type noise from the front end when accelerating after coasting (not pressing gas pedal at all). Happened almost every time that I re-applied the gas after coasting and was most noticeable when traveling under 40mpg.

The fix (directly from the dealership paperwork):
- "Checked for PI's and bulletins and found none. Inspected suspension and motor mounts and found all to be tight. Called GM technical assistance and spoke with [name omitted]. Case number [case omitted]. Was instructed to check front axle shaft splines for lack of lubrication and torque. With vehicle on lift and moving front wheels back and forth, the axle shafts are clunking where axle splines meet hub bearing. Lubricated axle splines and re-torqued axle nut to hub bearing. Test drove after repairs and no abnormal noise was heard."

Like I said, hopefully this may help someone else in the future.

Just curious - what would cause this type of situation to occur in the first place at only 19k? Possibly just a lack of lubrication and/or torque @ the factory?

Thanks!
 

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8th Gen Antagonist
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Weird... I usually put some anti-seize on the splines anyway, but weird.
 

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Discussion Starter · #3 ·
Thanks for the reply - any idea what might have caused this situation to begin with at only 19k miles?? The only thing that I can figure is that it wasn't properly lubricated and/or torqued at the factory? Just trying to learn here....

The dealership originally assumed it was an engine mount from the sound it was making - if that gives you any type of indication as to what it sounded like...

Thanks again!

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Maybe rust? I don't know, as long as its fixed and you didn't have to pay!
 

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Discussion Starter · #5 ·
Yep, was fixed for free under the factory warranty - haven't heard the noise since... They even gave me a loaner car since I dropped it off on a Friday and they were closed on Saturday and Sunday! :) Pretty cool since I didn't even but the car from them!

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Discussion Starter · #7 ·
Actually, no I didn't ask the dealer what may have caused it - I wish I did, to be honest... I'm guessing that it was just not lubricated properly at the factory, but that's just a guess... Since yours may be doing the same thing with only 4k miles, I would think that it too may have left the factory with improper lubrication. Hopefully, you can get some kind of explanation when they look at yours - if so, please let us know!
 

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Just left our maintenance yard. The mechanic knew exactly what the problem was when I described it and when he heard it for himself. He said it is quite common in our fleet (1500 or so Impalas), even in the newer impalas with low miles. He didn't know why it occurs, other than his personal opinion of the impalas not holding up to what we use them for and being crap.

He replaced the CV axle nuts and put different washers on that he said are supposed to keep the nut from loosening up. That fixed the clunk. He said the lubrication isn't really the issue, it's the nuts loosening up. He said this isn't the first impala with such low mileage (4200) that he has seen do it...

I'm thinking maybe a quality control issue or something.
 

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Discussion Starter · #9 ·
Thanks for getting back to us with the info - I appreciate it!

Sounds like the lubrication had nothing to do with it and it was actually just the "torque" of the nut that is causing/fixing the problem. I'm surprised that the dealer that I took it to (a pretty large Chevy dealer) hasn't run into this before if its such a common (and recurring) problem... I'll definitely have to keep an eye (or an ear, to be exact) on the issue in case it comes back!

Thanks again.
 

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I honestly doubt most people even notice it or don't care. Although I could hear it if my windows were up, it only occurred at lower speeds. I spend quite a bit of time driving at low speeds with my windows down. Your average vehicle owner isn't borderline OCD like me and aren't car people (not that im an expert by any means). Hell I see people all the time driving around with noises coming out of their car that make me cringe.
 

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Discussion Starter · #11 ·
Very good point - I'm the same way (borderline OCD) about my vehicles, whereas my wife couldn't give a shit!! :)

I notice *every* little sound and vibration - sometimes I'm not sure if I'm being OCD about something or if it's really a problem...

To your point, my wife would have *never* noticed this "clunking" sound and would have driven it like that forever!
 

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Discussion Starter · #14 ·
You want to provide the information that I provided in the OP to the dealer, since this did not seem to be a very common problem. The large dealer where I had the service done actually had to call GM for help diagnosing this problem - maybe the info in the OP would help the dealer if it is the same problem that I had...
 

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Their are 3 clunk bulletins but Their is a TSB on the axle nuts TSB#11-03-08-001A. But it states that it is for a "Growl Type Noise Coming from Front of Vehicle" but I can see a clunk happening as well but It will not show up when searching for a clunk. The cause is a loss of preload on the front wheel bearings. The fix is to replace the axle shaft nut, and if you have the police package you will need Nord-Lock washers as well, and torque the nuts to 220 Nm (162 lb ft).
 

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Discussion Starter · #18 ·
Also, per the OP, the clunk that I had didn't even have any associated PI or TSB's - but it does seem to be a somewhat-common issue according to at least one other fleet manager in this thread. Basically, just requires re-torquing some bolts, I believe (would have to check the first post in this thread for details).

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Discussion Starter · #19 · (Edited)
You know - I wonder if my clunk when re-accelerating at low speeds is just the same issue that I had in the OP of this thread again (axle shaft spline bolts needed re-torqued). I had this issue when I first got my car and had it fixed and I'm having what I believe to be the same issue again - never really put 2 and 2 together.

I believe that this issue should be covered under my 100k mile powertrain warranty, so I think I'll set up an appointment and have this same dealer check it again. If this is the cause, that would explain why some have the issue and some don't - and might help others that do have the issue.

I've addressed it via HPTuners (which so far works perfectly!), but if something just needs tightened, I might as well fix the problem instead of working around it.

Will report back...

EDIT: Hmm - are the axle shaft spline bolts something that I can easily try to re-torque myself? I'm not sure if they are something you can see and access just by removing the wheel or what. If it's easy enough, I'd probably just check them myself.

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Yes, the nuts are easy to get at with the wheels off. You will need a pretty good torque wrench to get up to 162 ft. lbs. Also you will need someone to hold their foot on the brakes while you tighten the nuts.
 
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