High speed vibration - need help tracking down

[G2]

Preferred reason for not using the stock (I believe) 75w90?

Thicker oil dampens noise. Its more appropriate for the high torque. Will only use 75-90
on a stock 4cyl or 6cyl car.

Have ealao used 190. Haven't tried the 250wt yet...

[lswing]

Thicker oil dampens noise. Its more appropriate for the high torque. Will only use 75-90
on a stock 4cyl or 6cyl car.

Have ealao used 190. Haven't tried the 250wt yet...

Aha, thanks.

Had vibration caused by out of balance tires, and then worn bushings on front control arms, couple possible causes.

[G2]

Aha, thanks.

Had vibration caused by out of balance tires, and then worn bushings on front control arms, couple possible causes.

Don't think these are related to the OP comments, but never know. If/when your tires are balanced again, be sure they are 'hot balanced'. Numbnuts Big Box Retail tires shops used to make my balance worse 1/2 the time. I have high tech tire machines. I can usually get a nice non bent wheel assembly down to 1 gram on both wheel planes. Don't know of a single shop that does a High Resolution balance. Industry standard 7gram. Not adequate or acceptable for an Audi. Use RoadForce, assuming they can get it down to 3 grams. Cheap tires don't help. Get tires balanced every 5K miles or 1X per year min.

Anything over 3-4 grams and I'm feeling it. Most people don't/can't notice it. In the long run your suspension, wheel bearings and shocks sure will. Here's where I say "ask me how I know".

Worn suspension won't per se cause vibrations. Surely will exacerbate it.

[fukinavit]

Thicker oil dampens noise. Its more appropriate for the high torque. Will only use 75-90
on a stock 4cyl or 6cyl car.

Have ealao used 190. Haven't tried the 250wt yet...

Be careful on thicker grades, i would stick with stock grades and change more regularly. sure a thicker grade might quieten the diff a tad but unless your towing lots, drag racing or living in a very hot climate year round best to stay away.
pretty common here in the winter to drop between minus 25-30 deg c, a thicker oil will offer zero protection until warmed up properly and on short drives will probably never get near its operating temperature.

[G2]

Be careful on thicker grades, i would stick with stock grades and change more regularly. sure a thicker grade might quieten the diff a tad but unless your towing lots, drag racing or living in a very hot climate year round best to stay away.
pretty common here in the winter to drop between minus 25-30 deg c, a thicker oil will offer zero protection until warmed up properly and on short drives will probably never get near its operating temperature.

Sure its common sense to think about what viscosity to use, especially when extreme cold is a factor. The issue of protection is always in hot conditions, when oil thins out. The rear diff gets surprisingly hot, not just from all the power. The exhaust pipes are right next to it, radiating tremendous heat. Similar situation for the center diff, with the cats right beneath. Main reason the seals leak oil. They get cooked. I've racked my car countless times after a drive and am always surprised at how hot everything is.

I don't want to rebuild a differential if it can be avoided. The oil I use is a cheap hold over fix. Five plus years on one car. Same situation on the transmissions; three should have been junked by now, including my own. All 3 to 5+yrs. Not simply thicker, but simply better oil.

Next time someone drains the gear oil and it looks questionable, will the status quo OEM spec suffice? Is being put in a box by OEM builders who's sole purpose is to get said vehicle past warranty, and to meet/beat CAFE (fuel MPG) standards, really worth listening too? Remember, there's Bean Counters involved. Thicker oil cost more.

Guess my question is what is the basis for recommending against, if anything other than a climate concern?