G50: Colder weather vibration---needs the experts here!

[Peterofdevon]

I (still) have a vib issue that needs to be diagnosed by the superior thinking power on this site

The vib usually occurs when the temp is under 50 degress. I believe its comming from the rear of the car. Car has new drive shaft, exhust hangers, motor mounts and transmission mounts.

Its a grinding vibration that comes on at over 20 mph and stays with the car through 80+ mph (it never fully goes away---but the faster you go the lees you feel it. The vib has a deep low pitched hum as well.

Last year Wes and I thought it could be diff bearings. I forgot about it as we went into the summer---it went away completely. Now its back with the colder weather.

I'm wondering also if rear wheel bearings could be the cause. Would they act up in the cold?

Amy ideas?

Peter

[Peterofdevon]

Does anybody read this board?

My post was moved here grrrrrrr....

no response from anyone one!

please help me with this

Peter

[maxnix]

I think we need more data.

It is quite possible that the lubrication of a bearing does not distribute when it is congealed by colder weather. Have you tried hand turning each wheel while the car is on a lift? Maybe use a stethoscope to listen?

If rear end lube is up to snuff, I can't emagine it would be different in cold or hot weather as it would be up to temperature after a few miles.
Modified by maxnix at 6:22 AM 3/10/2007

[elwesso]

Sorry peter.. Ive been busy and have been thinking about this.

seems to me the colder weather indicates something that changes with temp (duh). Rubber changes a lot with cold weather, metal does not in this case...

What rubber parts have you replaced? Exhaust hangers, diff bushigns, transmission mounts, etc????

[silkysmoothyjud]

It's not that we're ignoring you. Thats a tough one, might be differential? I've never had such a problem. It's purely a guess situation for me hoss.

[maxnix]

Certainly the new drive shaft included a new center bearing?

Have you indexed the shaft? Balance the assemble at a local shop that specializes in drivetrain balancing.

[Q45tech]

We always just use a lift and drive to speed and listen and observe and then focus in with a stethoscope.

Truck dyno with a pit so tech can get below the normal ride height with rear wheels turning dyno roller is a good think to have available.

[CaptinFocker]

Im not an expert sorry but I have the same problem only it happens at around 1700 rpms and I know exactly the noise your talking about. I have a feeling its the exaust. My reason I had to reaplace the exaust for it to go away but my case could be totally different.

[maxnix]

Usually third motor (transmission) mount with exhaust bracket and/or hangers is sufficient.

[silkysmoothyjud]

Ok bud, you just lucked out I think. Now that its getting warmer in Missouri Ive noticed that my car is a lot smoother. Therefore, Wes was right about it being rubber.....It's more than likely your tires. Either your getting crud stuck in em in the winter, or the rubber on your tires is hardening from cold weather. I've got seventeen inch wheels sitting on low profile tires. Ive noticed the noise from my tires have decreased in warmer weather as well (first winter with my new ride). I only paid 425 Dollars for my set of Hankook Ventus tires. I thought I really jacked up my alignment when I did my tie rod boots until it got warm outside. Do you have low profile tires on your Q? If you do, then I would say there's at least part your problem: 99.9% sure. When's the last time you've dropped your transmission pan and/or put in four fresh quarts?
Modified by silkysmoothyjud at 10:18 PM 3/18/2007

[silkysmoothyjud]

Alright, just updating. After my vibrations stopped, they came back in a big sort of way. After an inspection, I found that a blade broke off my radiator fan. I have not replaced it yet, but my car will sit until it is repaired, since it could damage my water pump....

[silkysmoothyjud]

The fan is replaced, all is well for now, but I need some rotors and some Tokico blues for my ride for sure. It looks stylin lowered, but I'd rather be smooooth baba! Don't EVER buy cheap rotors. Gimmie some of that nuegget (the stuff inside of twix bars)!! I'm lookin into candy painting my Q, local painter quoted me 450 for that fly paint alone....