Help: Car is vibrating at 75-85km/h

Hi,

 

I tried searching this but it seems nobody is having the exact same problem I am. So any help or insight would be awesome.

 

I own a 1998 Subaru Legacy Outback 2.5 manual transmission wagon with 149,000 miles on it. I have regularly maintained the car.

 

This problem is very erratic, and only happens when it is <0 degrees Celsius outside, and is EXTREMELY bad if it is colder than -20. My car will vibrate, at 70-90km per hour when it is cold and once the car warms up the vibration lessens to an extent. When it is vibrating, it sounds like someone has the window open on the highway, or like someone has low resonance subs playing. Also the vibration is not noticeable in the steering wheel or shifter (as it is a manual) it more so seems to come from the seat. Once it hits about 100 km/hr its smooth and disappears for the most part. Because it lessens once the car warms up leads me to believe that it has to do with lubrication. In the summer the vibration literally disappears and is not noticeable. (I do have summer and winter tires so i tried the summers in the winter to see if it was misbalanced rims or something and this is not the case, it still vibrated)

 

Here's what I have done:

-Tires balanced -> way to many times to count

-Brakes replaced (found out my rotors were a tad warped and with the cold weather the pads might have been sticking once depressed and would rub the rotors unevenly which may have created the noise......Turns out that was not the problem

- Changed all fluids in tranny and diff

- replaced clutch, although didn't machine the flywheel.

 

Here's what I think it is:

- Possibly driveshaft balance (although the guy at the shop said it was good)

- Wheel bearings (when car is raised and I try to tilt the wheels and they dont so it appears to be ok. Also a wheel bearing issue would be apparent throughout the whole speedometer range, and would not disappear at a certain speed so this puzzles me)

- Trans axles (I had to remove these to do the clutch but I marked them and placed them back in the same position as they were from the factory)

- CV joints, although they dont appear to have cracked boots

- Rear differential or something moving in the back section

- Alignment? (I had it done back in 2010-11 ish)

 

Please let me know what you think, I am clueless as to what is causing this problem and it is very annoying driving on secondary highways with speed limits of 80km/hr. I would appreciate any help I can get. I take very good care of my car and try to keep it in pristine condition so if I could solve this problem it would be much appreciated.

 

Thanks

Sounds like your tires are flat-spotting and causing issues at those temps.

what are the tires your running? That would be my suggestion too.

I had a little off road jump with mine wagon and bumped a piece of rock .At firs I didn't notice change but when I hit road and speed increase ....O boy. loud noise and vibrations .I look under the car and find the spot witch got hit .It was a bushing right under rear seat.I thing that it somehow isolate the chasy from cabine.???? I strait it up with bar and pair of pliers all good .It won't hurt to check.Good luck!

Stuck brake caliper caused similar vibrations around that speed.. easy check is to feel the warmth of your wheels after a drive if one is hotter than the others

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I was gonna say tires too when i saw the weather comment....but with the fact that you were running winters and tried your summers with no success, I guess flat spots are out of the equation for the most part.

 

You said it feels like chassis vibration rather then steering....any bias on vibration being from front or rear of the car?

 

Could this be a bushing issue? I know some people say the rubber in bushings will contract being cold then expand once warmed up.

Did you mention getting it realigned?