low-frequency vibration

[rtp373]

2002 OBW, 5-spd, 35,000 mi:

 

When I operate the car between 40-45 mph, the car vibrates noticeably (must be, the wife notices it too!). Also notice every deep crack in the road or bump sounds "louder" than it used too when you drive over it. The vibration is audible and is even more prevalent in 4th gear at this speed, possibly the vibration matches the normal vibration from the motor at this rpm? just a guess.

 

Tire pressures are all equal.

 

Would anyone suspect alignment and/or balancing issues...or anything to do with the AWD system?

[alias20035]

Originally posted by rtp373

2002 OBW, 5-spd, 35,000 mi:

 

When I operate the car between 40-45 mph, the car vibrates noticeably (must be, the wife notices it too!). Also notice every deep crack in the road or bump sounds "louder" than it used too when you drive over it. The vibration is audible and is even more prevalent in 4th gear at this speed, possibly the vibration matches the normal vibration from the motor at this rpm? just a guess.

 

Tire pressures are all equal.

 

Would anyone suspect alignment and/or balancing issues...or anything to do with the AWD system?

 

Check for loose hood deflector or windshield molding. Both can vibrate and really shake the car starting at about this speed. Also are your roof rack cross bars oriented correctly? Fat part of the cross bar is forward!! It is amazing the vibration that a simple loose hood deflector can cause, it actually can produce vibration as bad as a bent driveshaft! With the hood deflector it is essential that the rubber stick on pads be stuck to the hood and not the deflector itself, most dealers install the rubber bumpers incorrectly to the deflector because apparently they are illiterate when it comes to reading instructions. If the rubber bumper are on the deflector you can get a high speed vibration and worse than that you will quickly wear out the paint on the hood wear the bumper rubs (which is the real reason to attach this to the hood).

 

Since you have a bump related sound you could also have a bad transmission mount or pitching arm, both are common failures.

 

For vibration you should rule out aerodynamic items such as roof rack, hood deflector, etc first, simply because this is easy to do and a far more common problem then most people would beleive. Then move from tires to drivetrain, tires, CV joints/axles, differentials, driveshaft, transmission and mounts, clutch is generally the order to follow to trace this problem.

 

You've covered tire pressure, but how about a tire problem such as a broken belt or bulge in the tire or other tire damage? Does the sound eminate from any particular corner of the car?

 

Wheel bearings are common failures, but usually you have a high pitched whine for several months before it progresses into a vibration type rumble, although front wheel bearings can go from whine to rumble in a week or less. Is the vibration affected by turning? Is so it could indicate a problem with one of the front wheel bearings.

 

Is the vibration felt in the steering wheel or the seat of your pants? Generally if steering wheel it is a front wheel related problem, while the seat of your pants vibration is usually rear wheel or drivetrain related.

[rtp373]

No hood deflector, roof rack is factory-mounted and hasn't been altered since owning the car.

 

I have noticed it since my last oil change at the dealer, when I had the tires rotated. Maybe there's an off-balance tire that's more noticeable in the back?

 

I did a test and while coasting it was still there in this speed range. If I just pass thru this range I don't hear it, it's only if I stay at that speed range for more than a couple of seconds. I hear it more in 4th gear at this speed but I given the rumble of the subaru engine, it may just be harmonizing.

 

Thanks for the insight, I need to take it in again in the next couple of weeks for another oil change and to check it over before 36,000 mi.

 

Ryan

[charlierh2]

i have a 97 Legacy and it had the same problem. It was caused by worn out rear struts which i doubt in your case as it is a 2002 but i think this happened at maybe 80,000 for me so if your getting up there maybe something to check.

[cookie]

an out of balance condition can cause issues like this and so can a bent rim or a bump in the tire.

It is also possible that you notice it becuse it is on a different end.

First unrotate the tire and see if there is a change. While you have it on a lift inspect the tires carefully.

I once took a car to severalt tire stores before someone found the flat spot that was bothering me. They kept putting it on the balance machine and since it was in balance it must be round.

[intrigueing]

Try pressing the brakes lightly when it is making the noise to see if the noise goes away, I had brakes giving me the exact symptom you are speaking of.