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Discussion Starter · #1 ·
Hi,

I have a 2009 G8 GT, 1SC options package, had it for about 40 days and the GM dealer I bought it from has been trying to diagnose a vibration. They've re-balanced, done a road-force balance, switched out different tires/rims, etc, but it still persists, sometimes you feel it in the steering wheel, sometimes the whole car vibrates, speeds vary at which it occurs, but is generally from 70km/h and up. Could this be a driveshaft issue? Anyone else experiencing this? The Dealer is going to help for sure, but just thought I might not be the only one... Thoughts?

Other than that, car is an overall amazing value and vehicle, I love the space as I am quite tall and people can still fit in the back, and hey.... gotta love the V8. (Getting decent gas mileage, too!)

Also, has anyone added subs/amp? I don't want to mess with the dash, but it defintely needs a more well-rounded stereo.

Thanks!
 

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Most vibration issues have been cured with what has already been done to your car. Considering they swapped out wheels/tires I would tentatively eliminate that as the problem. Driveshafts also are balanced when manufactured, that would be a place to look. Also this is a wild-out-there suggestion but it has happened on at least one vehicle - the cars come with shipping blocks in the suspension that are supposed to be removed possibly before they get to dealer, maybe by dealer. Also the tires come overloaded with air for shipment, which also at some point needs adjustment.

That's all I've got, welcome to the forum.
 

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Discussion Starter · #3 ·
Thanks for the feedback. GM recently issued a service bulletin that indicates there may be a driveline issue of some kind, but I don't know specifics, the car is in the shop today and will hopefully be all good.

Thanks,
Ryad
 

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Discussion Starter · #4 ·
Getting there....

Hi all,

I've seen several posts on the internet from G8 GT owners having the same issue of a vibration, and as mentioned in my previous posts, GM issued a bulletin relating to the drivetrain, but it did not fix my G8. After 2 Road Force Balances and several adt'l trips to the dealer for other attemps to repair, they have finally acknowledged that there are 2 faulty tires, Goodyear Eagle RS-A's and as per many other posts online, the tire problem appears to be quite prevalent. This is eaither due to the 60 day shipping process from Austrailia or the tires are just poor quality, but either way my dealer is replacing 2 tires asap, and I am thinking this should solve the problem based on all the info out there and based on my G8's vibration.

Anyways, just wanted to update, as it's been a frustrating 2 months of ownership thus far, but other than that the car is amazing.

Ryad
 

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I had the same issue, I never reported he problem to the dealer, I just assumed it was poor balancing on the factory wheels. I really didn't care much since I had new wheels on order for it anyway. However, now with the new wheels, it still has the same issue.

Any updates on this issue before i take it in???
 

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Discussion Starter · #6 ·
Hi,

The 2 tires they ordered for me are finally in, I am booked in for Monday to have them installed and will update this post to verify if it fixed the problem.

Ryad
 

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Discussion Starter · #8 ·
Quite bad. I guess some drivers might not notice it depending on the road conditions, but it gets better/worse depending on air temp, tire temp, etc.
They've re-balanced the driveshaft, done road forces, switched wheels, etc, but thankfully they finally were able to condemn two tires. It is most noticeable at speeds of 70km/h up and generally gets worse at higher speeds. Sometimes the entire car shakes, sometimes it is felt in the steering wheel, sometimes both. Just glad the dealership is not giving up and won't give up. There are many other posts online pertaining to this on G8's, which is interesting.

Are you having the same problem?

Ryad
 

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No, I'm only getting get the DoD vibration which I feel in the steering wheel. Also, I heard that drive train related vibration (sounds like what you are experiencing) was in the non-sport package G8's.
 

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Discussion Starter · #10 ·
Getting there...

Hi all,

Just updating my post...Got 2 new tires, same make, etc, and the vibration is almost gone so it is clearly the tires, 100%. Unfortunately, the 2 new tires are of such a different quality than the old ones (Goodyear Eagle RS-A 18's) that it now feels like there are 2 completely different sets of tires on the car. They're going to try and install both of them on the back, then the front to make extra sure, as they installed one on the back and one on the front initially. Either way, I am pleased to announce that it has nothing to do with anything mechanical, and the dealer is going to continue to make it right.

I'll update when it's all good!

Long live the North American Auto Industry!

Ryad
 

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i just bought a used g8 gt, and it has a part throttle vibration.

it acts/sounds like the trans is slipping. it only happens at very light acceleration/deceleration. if you give it a little more gas it goes away.

i've never had an electronic trans before and don't know if it's normal or not.

i've tried searching the forums here, but i'm a noob and couldn't find anything.

any suggestions, or should i take it to the dealer?
 

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Here is the full bulletin. It is under Bulletins, Campaigns or Preliminary Information from SI2000. Hope this helps and gets the info out.
#PIC4989: Drive Line Boom Noise And/Or Vibration - (Oct 2, 2008)

Subject: Drive Line Boom Noise and/or Vibration

Models: 2008-2009 Pontiac G8
--------------------------------------------------------------------------------
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
There may be a either a boom noise or vibration and in some cases both a noise & vibration detected in a very few 2008 & 2009 G8's. This condition may be detected by customers at speeds of 55-65 MPH on either 08 or 09 G8's. The noise could be described as a low frequency boom or moan noise (not a whine) coming through the body. The vibration is generally felt in the seat or the floor pan. The condition could be caused by either a misaligned center support bearing assembly or the prop shaft mounting to the differential yoke.

Recommendation/Instructions:
The prop shaft center support mount is slotted left to right and can be adjusted by loosening the bolts which are accessible through holes in the metal shield between the prop shaft & the floor sheet metal. After loosening the center support bolts you can use a pry bar between the prop shaft & floor to adjust the center support. If the alignment isn't correct the prop shaft will usually "snap over" into proper location with very little input.

If the condition is both noise & vibration felt through the floor, re-indexing the prop shaft to the differential yoke may have to be performed:

Mark the relative alignment of the propshaft, rubber coupling, and differential in the original position.
Number the nut and bolt pairs and their hole in the rubber coupling which join the rubber coupling to the differential (silver) and the nut and bolts which join the propshaft to the rubber coupling (black).
Remove rubber coupling from differential and propshaft, ensure the nut and bolt pairs are kept together.
Re-assemble indexing the rubber coupling and silver bolts clockwise (relative to differential), and the propshaft and black bolts counter clockwise (relative to differential).
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
You can do this yourself, but the dealer will do it for free.
 

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We have had our 09 GT for less than one week and have noticed a small vibration around 55-60 MPH. Nothing to bother me at this time. I first thought it probably was due to the car being on the dealers lot for a while.
Irrespective, I will pay close attention to this and report if it gets to the point where I have to take it in for service.
I Love this CAR!
POPSG8GT
 

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At low load under part throttle you may be noticing teh 4 cylinder mode of AFM. If you can duplicate it at various steaedy state speeds under 76 mph and it always goes away when you step on it then that's what you feel, it is normal, and the only way to make it go away is to buy an aftermarket tune that turns off AFM.
 

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Hi all,

I have been experiencing the exact same condition with my G8 GT since I got it 2 months ago. The dealership has balanced, road force balanced and replaced all 4 Goodyear tires with Michelins. Still, the problem persists. The vibration in my car only seems to happen at speeds close to the programmed shifting points. Most noticeable at 60 - 70 km/hr (35 - 40 mph). No vibration at highway speeds. My Dealership has no idea how to correct the problem. They contacted the Regional Engineering Branch (here in Canada) and they had no solution so the Regional Branch has contacted the factory in Australia to see if they know of a solution. That was over 3 weeks ago and I'm still waiting.

Personally, not that I am a mechanic, but it feels like the transmission program/computer is trying to decide to shift up (or down) but isn't sure if it should and causes the transmission to vibrate. At first I put the blame on the AFM but at this point I am uncertain. If I am feeling the vibration I can put the tranny into sport mode and the vibration goes away. Sport mode has a higher (and posisbly tighter...not certain) rpm range so the shifting decision for the computer is made. The other thing is that I don't have any vibration at highway speeds while AFM is on.

I don't know about anyone else but over the last few weeks I have noticed that the vibration is occurring more frequently and is more intense. Hopefully the vibration isn't damaging the transmission.
 

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Vibration Update

Just providing an update regarding my vibration issue. I have been waiting since May 11th for something to be done since the new tires did not correct the problem. GM Canada gave me a call on Monday (after I called and left them a message) and told me that they would send out a field engineer to have a look at my car. I was told it would take about a week for that to happen. Well, I received a call yesterday at work from my Dealer asking if I would be able to bring the car in before lunch as the field engineer would be here that afternoon. I was told that it may be ready today but they could be sure and it may take until Monday. Since the field engineer wasn't there when I dropped my car off I have no idea what they intend to do or if they can actually do anything to cure the vibration. At this point I am pretty sure it is an AFM issue. I'll provide an update as soon as I get my car back
 

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I just put a call into my Dealer. The field engineer is recommending replacement of the engine and trany mounts. Of course these aren't stock items so I have to wait until they arrive. My own gut feeling is that they will replace the stock ones with ones that provide more dampening in hopes that the vibration won't be felt as opposed to actually fixing the vibration. Again, I will update when the new mounts are installed.
 

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Discussion Starter · #18 ·
Hi all,

Just wanted to provide an update as I started this thread back in 2008 and am still enjoying my G8 GT, but with substantially less vibration if any at all in most cases. It all came down to improper wheel balancing over and over and over. To this day, it is still not 100% balanced, but is 99% perfect. I had to take it to several private wheel and tire places as the dealer network just didn't care, or employed people with the less than required skills to do the job right. I don't think the Goodyear Eagle RS-A's are as horrible as I had originally thought, but I am happy to say I am rolling on Kuhmo Ecsta SPT summer tires which made a massive difference in ride and handling as well as getting off the line. Anywho, I am glad to say it has absolutely nothing to do with DOD, TCM, driveshaft, mounts or any other of the potential things it could've been based on the other posts. The only thing that is quite evident, is that tempurature is a huge factor in the vibration or lack thereof, even after waiting for the tires to warm up. (is it possible that the alloy used for the wheels is just extra sensitive to tempurature or that they're just extra sensitve to wind and road vibration?...I have no idea how or why as I am not an expert). Either way, it's all good, the G8 is likely to become a modern day collectible due to Pontiac's demise and the GXP is not coming to Canada which helps with the values as well. I'll update again, thanks to all who've responded as the feedback was helpful.

Ryad
 

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Discussion Starter · #19 ·
Update!!

Hi all,

Just wanted to provide an update as I started this thread back in 2008 and am still enjoying my G8 GT, but with substantially less vibration if any at all in most cases. It all came down to improper wheel balancing over and over and over. To this day, it is still not 100% balanced, but is 99% perfect. I had to take it to several private wheel and tire places as the dealer network just didn't care, or employed people with the less than required skills to do the job right. I don't think the Goodyear Eagle RS-A's are as horrible as I had originally thought, but I am happy to say I am rolling on Kuhmo Ecsta SPT summer tires which made a massive difference in ride and handling as well as getting off the line. Anywho, I am glad to say it has absolutely nothing to do with DOD, TCM, driveshaft, mounts or any other of the potential things it could've been based on the other posts. The only thing that is quite evident, is that tempurature is a huge factor in the vibration or lack thereof, even after waiting for the tires to warm up. (is it possible that the alloy used for the wheels is just extra sensitive to tempurature or that they're just extra sensitve to wind and road vibration?...I have no idea how or why as I am not an expert). Either way, it's all good, the G8 is likely to become a modern day collectible due to Pontiac's demise and the GXP is not coming to Canada which helps with the values as well. I'll update again, thanks to all who've responded as the feedback was helpful.

Ryad
 

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Discussion Starter · #20 ·
oops, sorry Mr. Moderator, not sure how I managed to post this twice in the wrong spot, meant to post it at the end of the thread...... sorry guys!!!

Hi all,

Just wanted to provide an update as I started this thread back in 2008 and am still enjoying my G8 GT, but with substantially less vibration if any at all in most cases. It all came down to improper wheel balancing over and over and over. To this day, it is still not 100% balanced, but is 99% perfect. I had to take it to several private wheel and tire places as the dealer network just didn't care, or employed people with the less than required skills to do the job right. I don't think the Goodyear Eagle RS-A's are as horrible as I had originally thought, but I am happy to say I am rolling on Kuhmo Ecsta SPT summer tires which made a massive difference in ride and handling as well as getting off the line. Anywho, I am glad to say it has absolutely nothing to do with DOD, TCM, driveshaft, mounts or any other of the potential things it could've been based on the other posts. The only thing that is quite evident, is that tempurature is a huge factor in the vibration or lack thereof, even after waiting for the tires to warm up. (is it possible that the alloy used for the wheels is just extra sensitive to tempurature or that they're just extra sensitve to wind and road vibration?...I have no idea how or why as I am not an expert). Either way, it's all good, the G8 is likely to become a modern day collectible due to Pontiac's demise and the GXP is not coming to Canada which helps with the values as well. I'll update again, thanks to all who've responded as the feedback was helpful.

Ryad


;)
 
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