Intermittent Vibration at Highway Speed

[dozndav]

Would any of you know what can cause an intermittent vibration at highway speeds? This problem happens around 60mph and continues to get worse as speed increases. I have a 2000 A6 2.7T manual. Only variable that is correlated with vibration is speed, I can be in any gear or even in neutral. The wheels have been balanced and worked well before on a previous car. I have also replaced one front control arm recently that was clearly worn trying to fix the problem to no prevail.

[jcman]

Originally Posted by dozndav

Would any of you know what can cause an intermittent vibration at highway speeds? This problem happens around 60mph and continues to get worse as speed increases. I have a 2000 A6 2.7T manual. Only variable that is correlated with vibration is speed, I can be in any gear or even in neutral. The wheels have been balanced and worked well before on a previous car. I have also replaced one front control arm recently that was clearly worn trying to fix the problem to no prevail.

Are they OEM stock rims?
Are the tires rotational?

[SloopJohnB@mac.com]

Get them rebalanced on a road force balancer...check the rims for runout.

Likely a bent wheel or bad tire/balance job. It's also possible the wheel is ok and the tire is balanced but the tire is defective/broken belt, etc. Road force balancer could sort it out.

[jcman]

Originally Posted by SloopJohnB@mac.com

Get them rebalanced on a road force balancer...check the rims for runout.

Likely a bent wheel or bad tire/balance job. It's also possible the wheel is ok and the tire is balanced but the tire is defective/broken belt, etc. Road force balancer could sort it out.

Second that too; after first two answers

[GTA_Driver]

You said "intermittently", meaning at times the vibration exists and at times it doesn't? If so, it's not the tires.

[Just Me]

these cars are ridiculously sensitive to balance and / or tire/wheel out of round. Its is 95% likely to be one of the three, and the fact that someone says "they are in balance" means almost nothing.

G

[SloopJohnB@mac.com]

Yes. The other thing is tire mfrs have different specifications for defective tires...for example one mfr may say 25lbf on a road force balancing machine is the limit, but the tire can only be balanced to 24 lbf. The car may shake like an epileptic dog in heat but the tire mfr says its within spec.


So do what you can to reduce road force to under 15 and preferably 10 (I've seen about 1-2 on new tires!) before you start working on the suspension.

[jcman]

Are you going to answer anyone?

[SloopJohnB@mac.com]

Sometimes it's more polite to allude to a possible solution, especially if the question is at best ambiguous. Many if not most of the questions asked on this forum have more than one answer; I prefer a discussion, an aha moment if possible.

[jcman]

Originally Posted by SloopJohnB@mac.com

Sometimes it's more polite to allude to a possible solution, especially if the question is at best ambiguous. Many if not most of the questions asked on this forum have more than one answer; I prefer a discussion, an aha moment if possible.

"Detective without curiosity is like glass eye at keyhole - no good."

My technical trade lends too much detective work that I have done over the past twenty plus years on commercial refrigeration and HVAC systems far more complex than cars along with commercial insurance consulting relative to my trade to stop fraud.

In any diagnostic tree there is always a yes or no after a question relative to a symptom or condition, some might prefer to throw out an answer or suggestive comment first to maybe strike-up an answer.

I prefer systematic diagnosing, and yes even though it may appear to be forward and less than diplomatic it some how works for me to help people with a problem and I make a good living at it too.

I am here because I like being here and believe I have much to share, I have told many young technicians that I have brought into my trade with this quote; "I am an answer guy not a question guy" but in reality I'm here because of the good questions.

So it be said.