Naf

iTrader: (1)

Can you specify if your butt vibrates or the steering wheel or both?

Could be an alignment issue.

VincentT

I had a similar issue two years ago, albeit at higher speeds (55-65). Driveshaft was perfectly balanced and indexed. Turned out to be a worn out OE trans mount. The drop in the mount misaligned the carrier bearing and driveshaft, creating a wobble. Revshift insert fixed it.

It made the rubber surrounding the carrier bearing look like it had collapsed, but the rubber there was fine once the trans mount was fixed.

RunYun

Check out the carrier bearing first. If you find a lot of play replace the driveshaft and bearing. If it is still there you likely have a damaged wheel. I chased the same issue for a good while. Replacing blown engine mount helped some then driveshaft then when I went to have new tires put on I had them check the wheels. Sure enough a bad wheel. It was not until I resolved the other issues that it became more obvious. Rotate your tires and you should be able to confirm a tire. Mine was slight and there was a very select sweet spot about 62 a 65 so it made it harder to pinpoint.

Good luck

wes8398

iTrader: (2)

Thanks for the input, guys. I need to learn where/what exactly this carrier bearing is and then have a look at it, for sure. It's officially on the Caddy to-do list.

RunYun - You missed in my OP where I said it's definitely not wheel/tire related. I've recently swapped over to my winters and the vibration stayed exactly the same. Appreciate the input, regardless. THanks.

VincentT - Interesting. I've had Max's (Creative Steel) "soft" trans mount installed for a few years now, so I shouldn't have the issue you described. I'll still keep this info in mind when I'm under there checking the carrier bearing out.

Naf - I can't single out exactly where the vibration is coming from, but it's not in the steering wheel. I can feel it and see it basically everywhere though. I can see the passenger seat shaking ever-so-slightly, I can feel/see it in the shifter, and I can feel it shakin' me through my seat. It's not like driving over rumble strips or anything, but I could maybe compare it to the feeling you get when you're driving on a highway that's not had the top coat of pavement laid down yet... where it's like corduroy...?

54inches

iTrader: (4)

How did you store the tires and wheels?

Naf

iTrader: (1)

they should have been laying on their side with air pressure...

Thats how i store mine for long periods of time

somethingclever

iTrader: (1)

wow was not thinking clearly when posting....wrong...very wrong.

wes8398

iTrader: (2)

Funny you guys should mention storage, because that was my first thought too. I used to stack our wheel mounted out-of-season tires on their sides on the garage floor (with a rubber tile under them, so the bottom tire wasn't touching the concrete). The summer before last I did a bit of a garage re-organization which included a set of wall mounted tire racks(see pic) that Santa had given me that Christmas. So my winters have sat in those racks for 2 summers now, and my summers have just started their 2nd winter in them. This vibration is new as late summer of this year;well after I'd started using these racks. And it's not new since putting my winters on; the vibration stayed the same with the summers and the winters on.

I thought maybe the bars that the tires rest on in those racks might've created little flat spots in the tires (even though there's hardly any weight on them and I keep them at ~50 psi when racked), so just to be sure, I brought them to my local go-to tire shop and had all 4 wheels put on the balancer (which they said also picks up flat spots on the tires). I was given the 'all clear' by them. Also worth mentioning is that the other vehicle's tires that sit in the 2nd rack haven't developed any issues from the racks either. So this is why I was saying that I didn't think this was a wheel/tire/balancing issue. Think it still could be?

Fweasel

iTrader: (6)

I keep three sets of wheels on those overhead racks for three different cars. Everything from snow tires to soft summer only compounds. I see a few marks on the tread when I pull them down at the end of the season, but have never had any vibration issues on any of the cars. I also over inflate the tires before storage as well.

rand49er

Wes, not sure I'm being much help here, but I had my carrier bearing checked once when I had my LS9 clutch installed, and the guy said it was fine. Guess I'm saying it's very easy to check and should be done just to quickly rule it out.

Any new developments?

wes8398

iTrader: (2)

Thanks for the reassurance! I was starting to contemplate taking the racks off the walls and selling them, just to stack my wheels back on the floor again.

Thanks Randy! If I see an open lift at my guy's shop when I'm driving by one day maybe I'll ask him to rack 'er up and take a quick peak. Otherwise, I planned on trying to have a look at it when I'm doing the PMC job. I'm just not sure when that's going to happen. Damn attached-but-not-insulated garage...

rand49er

I hear ya. Quickie oil change place said I've got a slight leak on the oil pan of my DD, and it's too blasted nippy for me to get out the Rhino ramps to see it for myself.

And, it's not even winter yet.

07CTS-V

iTrader: (6)

To be honest, I would loosen the two nuts that hold the trans mount to the crossmember, lift up on the trans and let it fall where it wants to, then tighten the two nuts back up.

If you tighten the mount/trans to the crossmember then the crossmember to the body, you'll sometimes get this vibration.

ls1247

iTrader: (2)

Words of wisdom...

wes8398

iTrader: (2)

Hmmm, this is a new and interesting angle. I remember when I put that trans mount in (way before all this clutch stuff), I had a helluva time with something... one of the mounting bolts maybe? I didn't have the exhaust dropped or anything, and I can just remember getting really frustrated with something.
Would it make any sense that when my shop did the clutch for me, they might've put things back together the (wrong) way you describe?
And you're just referring to undoing the 2 nuts that point down to the road, right? Is there a TQ spec for these? Or are you saying to let the bolt come through the x-member as much as it wants and then just snug things up (without tightening much)?

07CTS-V

iTrader: (6)

Those are the studs and nuts. Raise the car up, loosen those two nuts, wiggle the trans, tighten the two nuts. I don't use a torque wrench on them...German spec.

wes8398

iTrader: (2)

10-4, thanks for the tip. Certainly worth a shot anyway.