I have a 2005 GXP. From day one I've been feeling a vibration problem anywhere from 60-85mph. It comes and goes every 10 seconds, not too strong, but you can feel it in the seat. The steering wheel is not vibrating at all. Had the tires dynamically balanced-didn't help. Had the tires 'road forced balanced' by dealer - didn't help at all. The car has Goodyear Eagle RSA tires(235/50/18. I've seen many cars (Cadillac, Buick, Aurora) having similar problems, the common denominator seems to be with the RSA tires. Any one have a similar problem? Suggestions?

The first thing I'd try is rotating front to rear, but that likely happened during all that balancing. Maybe jack the car up and spin each tire, and try to move each around. Maybe a bad hub/bearing assembly? Most likely rear if you feel nothing in the steering.

Hmmmm, I only have about 2,000 miles on my GXP and every once in a while feel a vibration between 65-70 on very smooth blacktop, Any roughness in the road masks it. I thought it was my imagination until I read your post. No vibration in the steering wheel here either. I'm going to try rotating the tires front to back to see if the vibration will show up in the steering wheel. I'll post after I do that... probably not for another week.

If it does not show up I'll suspect the alignment and will take it back to the dealer.

I spent a lot of time troubleshooting this vibration problem. It appears to be also on the Aurora, LeSabre, some Caddy models(STS?), and Bonnevilles. Funny... all these models have been discontinued and also per the TSB that all these models share the same chassis. It turns out that the chassis is very sensitive to 'rotating masses' as stated in the TSB. GM can't readily solve this problem, but started throwing Michellin tires at the Caddy owners(back in 200-2002) to help lessen the problem. It solved some problems, but not others. The only cure for GM was to discontinue the models and avoid the issue. as much as possible. I personally think that the chassis is very stiff, and it shows as my GXP handles VERY WELL for a front wheel drive car with 60% of the weight in front.

I read the entire TSB and even after force balancing the tires, the problem did not go away on my car. I also concluded that I would have to make at least 6 trips to the dealer and deal with a lot of crap and stress, and only hear them say 'Its normal', I decided to solve the problem at my own expense. So I did a few things:

I marked all the rims with a number and rotated the tires(there are 16 possible combinations). After rotating one set, I test drove the car. After about the fourth rotation, the problem got better, but was still there. I also added up to approx 38 lbs of 'warm' air in the tires, but the problem stayed the same.

I was going to replace the RSA tires with Michellins, hoping that it was a bad belt somewhere, but the Michellin'* are expensive and it may not solve the problem.

I then left the configuration at the best possible rotation that reduced the problem the most. I then lowered the front tire pressures to 29lbs and rear to 28lbs(cold), and guess what???

The problem has been reduced by about 90%. It only vibes a bit at 82-83 mph, but before and after that, its all good. Even at over 100 mph, its quiet.

I hope this will help folks, as this tormented me for many sleepless nights, knowing that I just paid a crap load of $$ for a defective car. I can't believe GM can't even design and TEST a good chassis combination. I think it'* time for a turnaround in GM, else they will go bankrupt soon. If you guys can't make a decent, solid chassis, then OUTSOURCE IT!

I'm done...

Wow!!! Lots of homework, thanks.

I haven't tried any correction yet 'cuz the only time I get any sense of vibration is on one stretch of blacktop... and I'm not at all sure it isn't the road. I will take the SSEi out there one of these days to see if does the same thing. I think I've been over that stretch in the past with the SSEi and I don't remember any sense of vibration.

There is no question that the GXP has a tighter suspension and also the lower profile tires probably make a difference.

I only have about 2,600 miles on the GXP so it will be a while before I take it in for its first service call... but I will address the issue before then.

On a lighter note, I just got back from a circle thru Canada and New England in the Vette. I got a 20 minute run on a two lane mountain blacktop with no one in front of me. I had a blast, not so sure my buddy enjoyed it as much as I did. I almost have the MN6 (manual six speed) mastered. The first few weeks I had the car I thought I had made a terrible mistake... starting up from a stop was a grab bag of squealing tires or killed engine or being caught in a jerking paint mixer.... in no particular, or predictable order. Been a long time since I owned a manual transmission, and that was on a VW... and the C6 ain't a VW

I too have an 05 GXP. I've got just over 9K miles and it has exhibited a vibration beginning right at 60 since I drove it home. Of course, the dealer says it'* "normal" -- something about the 3:71 gear in the transaxle -- um, yeah. I've thought all along that it was the Goodyears, and I've had the re-balanced and rotated with no effect. I'm going to try the change in air pressure to see if that does anything.

This car has been pretty good, only a couple of things have happened, but the dealer isn't too swift about dealing with them. For example, the driver'* side rocker panel moulding came loose (close to falling completely off the car). They tried 3 times to basically duct-tape it back on. I finally got PO'd and had the Service Mgr look at it -- they ordered a new one and had their body shop put it on (imagine that, they were having a service tech do this when they should have taken it to their body shop in the first place.) Anyway, I mention this specifically because when I got the survey from GM, I sent it back with a letter describing the situation -- not expecting any kind of response, of course. Interestingly enough, I got a telephone call from Pontiac saying they opened a file on my complaint, had contacted the dealer, and asked me to return to the dealer and the problem would absolutely be fixed to my satisfaction. I did, and it was -- I was very impressed with the response from Pontiac -- they kicked their dealer in the rear to get them to take care of a problem.

Only other problem was on oil leak at about 5K miles -- proved to be a failed gasket under the oil filter adapter -- replaced under warranty of course, and no further problems.

Thanks for the post.

Transmission!!! Wow,

Well that explains why the SSEi and the Chevy don't have the vibration, huh?

Actually, I'm just not going to pursue the topic futher... the vibration is so very slight, it only occures at 60-65 on very smooth asphalt... and I rarely see smooth asphalt... and more important I never drive at 60-65

I have some new information that might be relevant to this conversation -- and I'll try not to get too long-winded in describing it. I took my 05 GXP to the dealer today because yesterday morning the transmission started shifting VERY hard -- like banging gears on a drag strip. (Oh yeah, I also had the driver'* side fog lamp replaced -- that was another topic on another message in this forum.) A "DTC" (error code) was stored indicating that the adaptive transmission shifting software got an intermittent signal and was unable to store the updated info for the transmission. Evidently the diagnostic computer indicates the sensor is good, so there is no certainty why this signal/data loss happened. (The immediate cure was to stop the car, shut if off, then restart it -- the computer reboots with trans module with the defaults -- shifts normally now.) The dealer'* service manager discussed this with me and said they are going to clear the code and if it does occur again then they'll start in on other tests on the trans. Anyway, something else interesting -- relevant to this message -- occurred. While the car was on the lift and hooked up to the diag computer, the service manager had the tech check all the motor mounts -- sure enough, one of the mounts is "bad". It is broken, per se, but it has a bunch of freeplay that isn't right. The service manager asked me if I noticed in vibration at any speed -- I told him about the 60-70 or so vibration and he believes it is a result of this bad motor mount. Anyway, they've ordered one and it'll be replaced next week -- we'll see if this fixes the vibration. One wonders why the service manager had the tech check the motor mounts in the first place -- maybe GM knows something that they're not ready to make public? BTW -- I tried the air pressure changes mentioned above, but the vibes in my car didn't change a bit. I'll post the results of the motor mount swap once this has been done. Interesting no?

WOW Again... if that turns out to be the fix this forum is worth it'* weight in gold!!!

Thanks very much for the info.

On a more light hearted note... look what I did this week

http://forums.corvetteforum.com/show...14&forum_id=74

Okay, the dealer did the motor mount swap today, but he also went ahead and re-balanced and rotated all four tires. My service writer tells me that they found both rear wheels were not properly balanced -- left was off a 1/2 oz, the right off 1/4 oz. He also told me that they drove the car before doing anything to get a baseline. The vibration was present at 58 mph on up to 70 -- pretty much a steady low-frequency vibration -- steering wheel only slightly affected -- they felt the vibration mostly in the seat of the pants. (I noted that I had paid a local tire specialty shop to re-balance them (not trusting the dealer'* equipment/staff), but that shop'* service did nothing to resolve the issue.) They then did the re-balance and rotation and on the subsequent road test -- voila, vibration gone. According to the writer, the motor mount was definitely defective -- the rubber portion allowed "way too much free play". Regardless, neither he nor the technician believe it had anything to do with the vibration -- I guess the service MANAGER'* call on the motor mount being the vibration culprit was a miss on his part.

I road-tested it myself on the way home -- smooth as glass all the way from stop to just over the century mark -- it seems to urge me to go faster, but not on the roads around here. You know, I've driven quite a few big cars and this Bonneville absolutely stands out. When it'* "on", it really is a joy to drive.

So, if you've got a GXP with a vibration, get your dealer to do a re-balance (or pay a quality tire shop to do it) -- it did the trick for my car.