Yesterday I made a post "XC tire options". While this one is related, I decided to make it separate because I believe the topic deserves its own thread. Again I apologize if this has been a much discussed issue in this forum. The reason behind wanting to replace my tires quickly is because of what seems to be a drivetrain noise, like a "whirring". It's rather difficult to pinpoint just when it started or how "different" from normal it is since the original Pirrelli ST's have never been very quiet. Still, my wife and I agree that it seems to be getting worse. To add to that, I recently felt some low level front end vibration that seemed to come on when starting to decelerate from about 65 mph. It only lasted for 10-15 seconds and may have been related to road surface, but I wouldn't bet on it. I tried to repeat it one time and thought I could feel it but was not sure. I considered the possibility of a wheel bearing but the whirring does not seem to change with the steering direction. It just seems to always be there while the car is moving, but does seems more noticeable at times. Knowing the sensitivity of the AWD system to tire dimensions/problems, I decided to change the tires as the first step. They have been rotated regularly but never balanced. They are not quite down to the wear bars and generally seem to have worn evenly. One thing worries me is that one tire picked up a nail and was found very low on air pressure several times before it was properly repaired. I am keeping my fingers crossed that no damage occurred to the infamous "bevel gear" or viscous coupling while driving with low air pressure in that one tire. I have heard war stories about this happening and the high repair cost involved.

I will post again on this subject once the tires are changed. In the meantime, any comments on my symptoms would be greatly appreciated. I know that one symptom of bevel gear failure is a leaking gearcase. Mine is currently dry, but I don't know if there are other symptoms such as my whirring noise.

 

Last week I changed out the tires with a set of Dunlop Sport A2 Plus's. GOOD NEWS! The reduction in the level of drivetrain noise was immediately obvious, returning to what was once normal. I believe I "dodged the bullet" in that I did not correct my leaking tire problem as promptly as I should have. Hope this serves to raise the consciousness of the owners of all such vehicles to the sensitivity of the full-time AWD system.

 

Glad the tires fixed it.