Vibration at 90 mph

**Naaman** · 03-11-2014, 06:26 AM

Okay, help me remember:

When a vibration comes through the seat at a specific speed, that is most likely something to do with a driveline imbalance, correct?

A coworker of mine asked me about his LS2 Corvette/M6, saying that he felt a viration at the "back" around 90-100 mph. Below that, it's not noticeable. He also says that the vibration is not "constant" but rather it occurs at a regular interval (kind of like the interval of the sound that a rock makes when it's stuck in your tire tread).

I THINK this is most likely an out-of-balance rotating part aft of the clutch (torque tube comes to mind, then again, that spins the same as the engine, and it doesn't appear to be RPM related, but rather road speed related), but I suppose it could also include the wheels themselves, no?

Suspension is stock.

Some other things that cause vibration that I'm aware of are:
Rotors
Alignment
... Could it have anything to do with the torque on the wheels/hubs?

I'm rusty, here...

***SMWS6TA*** · 03-11-2014, 06:53 AM

Could also be tire wear and pressure. More you drive the air changes in pressure. A slightly worn tire can give vibrations.

Start with the simple stuff first and then work up that list.

**35th-ANV-SS** · 03-11-2014, 10:52 AM

First things I would check for vibrations:

- tire out of balance (weight fell off)
- bad tire
- drive shaft out of balance

**Naaman** · 03-11-2014, 11:51 AM

Okay, so it seems like I was not far off on my initial assessment. I talked to him a minute ago and told him to check the wheel weights.

**sjgreen6** · 03-11-2014, 03:10 PM

Is this a daily driver or has the car sat through the winter? If it has been sitting it may be that the tires have taken a flat spot, especially if they are old tires. If so it will normally work out over a bit of time and getting the tires heated up to full temperature.

**cammed goat** · 03-11-2014, 04:54 PM

I also agree with the possible wheel weight loss and shifted belts in either of the rear tires.

**Naaman** · 03-11-2014, 04:56 PM

Okay, awesome.

Originally Posted by sjgreen6

Is this a daily driver or has the car sat through the winter? If it has been sitting it may be that the tires have taken a flat spot, especially if they are old tires. If so it will normally work out over a bit of time and getting the tires heated up to full temperature.

It's a daily driver, he bought it a month or so ago with I think 60K on the clock, or something... so who knows what it's been through. He bought it from the dealer, if that means anything...

**pajeff02** · 03-12-2014, 03:03 AM

Looks like the bases have been covered -- air pressure and wheel balance. One thing that hasn't been mentioned is to check the lugnuts to ensure that they are torqued properly. At the speed mentioned, the wheels are turning rather quickly so it would be kind of odd to hear a regular thrum. The wheels are probably making around 20 complete revolutions per second at 90 mph. Absent an apparent issue and a visual inspection of each tire being ok, it's probably time to hit the alignment rack.

**Naaman** · 03-13-2014, 02:53 PM

Originally Posted by pajeff02

Looks like the bases have been covered -- air pressure and wheel balance. One thing that hasn't been mentioned is to check the lugnuts to ensure that they are torqued properly. At the speed mentioned, the wheels are turning rather quickly so it would be kind of odd to hear a regular thrum. The wheels are probably making around 20 complete revolutions per second at 90 mph. Absent an apparent issue and a visual inspection of each tire being ok, it's probably time to hit the alignment rack.

I thought wheel torque might be the cause... anyway, the next day after I posted this, he said he could not duplicate the problem again... go figure...