Odd vibration at 85


#1

Guys – the oddest thing happened last week – and I am stumped! We had the misfortune to get invited to a friend’s house in the country, along with all the bugs, and we were flying down the interstate at the posted 70MPH limit. As we dipped on a long down grade hill, I thought I owed it to my 08 G35S Infinity to exercise its motor for just a bit. Quick scan for the local state troopers, and then I floored it… the car was very responsive and smooth, brand new tires humming just ride, the interstate pavement smooth as silk.

When we got to 80 MPH, the lip of the hood, closest to the windscreen, began to vibrate. We could hear it - and see it. And no, I was not eating country mushrooms, and my wife was right next to me and was puzzled by this. So I slowed down to 70 MPH, and it went away; I resumed back to 80 and it came right back. It was not a bad road vibration, did not feel like an unbalanced or damaged tire(s) – I experienced that vibration. This was nothing like it. So I pulled over the highway, and carefully walked around the car – looking for a trash bag, dead possum, and boot – what ever I could have dragged with me. Nada – nothing! The car was perfectly clean, especially underneath – nothing. I popped the hood – everything was right where it should be, nothing caught or trapped.

When I merged back into traffic, I pumped the engine high and fast at 4500+ RPMs to see perhaps if the issue was in the engine (unbalanced overhead cams, chain,…). Nope – engine was smooth as silk, quickly getting through the 6 gears and back to 80 MPH in no time. At 85, the hood began to vibrate loudly again – and we could see it harmonically oscillate apx ¼ inch up and the same down in rapid succession. It made a loud thud, dull roar inside the cabin. The wipers were tucked underneath and not in the slipstream. And the car is extremely aerodynamic – it looks like it was sculpted in a wind tunnel.

I asked several engineering friends, one of them a real rocket scientist (JPL spaceflight dude) – and they all looked at me like I was on crack. No clue. So, in an act of desperation, I took it to my friendly Infinity dealer – and their technicians really understand the vehicle from all angles. They looked puzzled as well – no such entry in the database, let along recalls on this issue. Suspecting it is the brand new tires, they mounted each tire on a sophisticated spin balance – and found out that all four times were significantly off balance (by 40 grams). Sounds plausible – until I took the car out again on the highway – and the same symptoms returned. I am stomped!


#2

Guys – the oddest thing happened last week – and I am stumped! We got invited to a friend’s house in the country, along with all the bugs and 8 smelly dogs, and we were flying down the interstate at the posted 70MPH limit. As we dipped on a long down grade hill, I thought I owed it to my 08 G35S Infinity to exercise its motor for just a bit. Quick scan for the local state troopers, and then I floored it… the car was very responsive and smooth, brand new tires humming just ride, the interstate pavement smooth as silk.

When we got to 80 MPH, the lip of the hood, closest to the windscreen, began to vibrate. We could hear it - and see it. And no, I was not eating country mushrooms, and my wife was right next to me and was puzzled by this. So I slowed down to 70 MPH, and it went away; I resumed back to 80 and it came right back. It was not a bad road vibration, did not feel like an unbalanced or damaged tire(s) – I experienced that vibration. This was nothing like it. So I pulled over the highway, and carefully walked around the car – looking for a trash bag, dead possum, and boot – what ever I could have dragged with me. Nada – nothing! The car was perfectly clean, especially underneath – nothing. I popped the hood – everything was right where it should be, nothing caught or trapped.

When I merged back into traffic, I pumped the engine high and fast at 4500+ RPMs to see perhaps if the issue was in the engine (unbalanced overhead cams, chain,…). Nope – engine was smooth as silk, quickly getting through the 6 gears and back to 80 MPH in no time. At 85, the hood began to vibrate loudly again – and we could see it harmonically oscillate apx ¼ inch up and the same down in rapid succession. It made a loud thud, dull roar inside the cabin. The wipers were tucked underneath and not in the slipstream. And the car is extremely aerodynamic – it looks like it was sculpted in a wind tunnel.

I asked several engineering friends, one of them a real rocket scientist (JPL spaceflight dude) – and they all looked at me like I was on crack. No clue. So, in an act of desperation, I took it to my friendly Infinity dealer – and their technicians really understand the vehicle from all angles. They looked puzzled as well – no such entry in the database, let along recalls on this issue. Suspecting it is the brand new tires, they mounted each tire on a sophisticated spin balance – and found out that all four times were significantly off balance (by 40 grams). Sounds plausible – until I took the car out again on the highway – and the same symptoms returned. I am stomped!


#3

Run a wide strip of masking tape across the gap between the hood and valence and test drive. Wind turbulence across misaligned panels can be quite dramatic.


#4

Two posts, same topic (and poster). See this one.