Hi,

I've perused G35Driver many times over the years but think this is my first post here, so forgive me if I make a mistake.

I have a 2006 G35X that I have owned since new. It currently has approximately 120k miles on it. I've been pretty religious about maintenance, including changing all driveline fluids every 30k. My wife drives the car daily so I only get relatively brief glimpses into how the car is driving and don't always know how long something has been going on.

For a while, I've been annoyed with what I'd call a groan at 65mph when coasting on the highway. It didn't bother her and didn't seem to be getting any worse, so I didn't lose too much sleep over it. It seems to get worse after you've been driving on the highway for a while, which makes me think it may be a differential or transfer case as the fluid changes viscosity with temp. My wife has also complained that the rear view mirror blurs to the point of being unusable when the engine is under load and vibrations in the passenger seat (when I drove) above 75mph).

Anyway, recent work on the car includes

1) changing the front propeller shaft from the transfer case to the front diff
2) New Michelin Premier A/S tires (I'm on the 17" stock wheel)
3) New struts and shocks (still on the originals at 120k)
4) New compression rod bushings
5) Alignment

1&2 were done about 5k miles before 3&4. The front prop shaft had play in the u joints and I thought the groan may have been a tire noise. Unfortunately 1&2 didn't fix any of the issues. The compression rod bushings were shot so I figured I'd change the shocks at the same time.

3,4,5 seem to have lessened the RVM blurring and passenger seat vibration, but it's still there. But it also introduced a new vibration. AT 75mph, with the engine under load, I can feel a vibration in the steering wheel that is engine RPM dependent. It's not to the point where you can see the wheel moving, but I can feel a vibration in the wheel that corresponds to the engine RPM - as the engine RPM increases, the vibration frequency does also.

I'm guessing that there was this vibration before and that the new bushings and shocks are simply transmitting a problem that was there before.

Sorry for the long post, but to summarize:

coasting groan from about 60-70mph, most prevalent at 65mph
RVM shake under engine load
Passenger seat vibration above 70-75mph
Steering Wheel vibration at 75mph with engine under load.

I would appreciate any thoughts as to likely causes. When I had the tires installed, I had them balanced, but perhaps they need to be rebalanced. Perhaps an out-of-round wheel that the tire shop didn't catch when they balanced them?

Thanks!

 

Have you checked your front wheel bearings?

 

Thanks for the thought. I too suspected wheel bearings but I don't think that's it because it doesn't seem to change when going around a turn. My understanding is that a bad bearing would be louder when that side was loaded. In other words, a right side wheel bearing would be louder when turning left and the weight was transferred to the right side.

I appreciate the thought

 

I know one of my wheel bearings are going bad because a tech specialist at a dealer had used a stethoscope to listen while the wheel was rotating and heard it grinding or making some noise, perhaps you can do the same because I know for the AWD G's they do seem to go bad most commonly around 100k miles.

I have the original service records from the previous owner and it looks like my front passenger bearing was replaced around 56k and that is the one that is acting up again now at 102k.

 

Check your front hub bearings as the other posted. You didn't hear noise but it may have made that indicator noise when wheel was turned and your wife wasn't paying attention. Mine hummed and groaned for months, turned wheel left and sound increased. Driving home the other day it became so bad that it felt like a flat tire and the steering wheel and car were shaking. It will not make the humming noise now leading me to believe it totally shot. I'll be busy this weekend changing the hub and bearing.

 

Not necessarily.

I've replaced 3 bad bearings on my car. ALL front. Not all of them exhibted that characteristic. 1 of them was the same no matter which way I turned. They didn't even move around like a bad wheel bearing typically does. Nice and tight with no wheel movement side to side or up and down.

Easy way to diagnose. Pull both front wheels on and remove the rotors. Turn the hub by hand. If it feels rough, it's bad. With the rotor and wheel on, you won't feel it but as soon as you turn that hub by hand you'll know if the bearing is bad. A good bearing feels smooth

 

duke, did you ever pin point the cause of the groan and vibrations?