Question about 1999 Subaru Legacy

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1999 Subaru Legacy GT - Front end humming

I have a 1999 Subaru Legacy GT AWD with 175,000mi. I purchased it without a Freeway drive.
Going home (all freeway), I noticed a slight humming at most speeds (barely audible).... figured it was the tires that were in need of changing.
Previous owner stated car was gone over with a fine tooth comb and replaced everything that was hinting of being bad.
Removed a wheel for closer inspection after arriving home because i suspected bad wheel bearings, and saw no problems. No looseness in the axle - lateral or vertical. No extra heat eminating from the bearings. Everything is tight.

1/2 shaft boots look new with no damage.

Axle retention nuts look new... as if the axles have been recently replaced.
Fluids are correct, and at proper levels.
Took a vacation road trip to FL, and as soon as we passed 40MPH, it sounded like permanent rumble strips were under the car!! But it was only evident thru the construction zones - thats why im baffled.

Between 40 and 60MPH we couldnt hold a conversation. After 60MPH its quiet as night!
This is an AWD vehicle - is there a torque converter or something else i can look into to resolve this? Driveaxle bearing?
The tires are brand new all season performance and balanced. We recently had snow, and the noise was still evident on ice/snow covered roads.

I did notice a slight lull when I went over railroad tracks @ 50 kind of BUMP JUMP. The noise lowered, but when the weight of the vehicle transferred back to the wheels, so did the sound.

The noise is constant during accelleration, coasting or braking - and stays constant even with the engine rpm fluctuation... (put it in N going 50, and revved engine.

No change in sound.

What is the noise, and how can it be repaired??

Posted by on

  • blueextc3221
    blueextc3221 May 21, 2009

    Dead on. Replaced the P/S bearing - and problem went away... but now i am hearing the rear on the same side to a lesser extent.

    Previous owner must have hit a big pothole to take out both bearings :D



    thanks again.

    Gave u the FixYa.

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  • Master
  • 1,596 Answers

@ 175K miles the Idea of Transaxel Output Carrier Bearings Should Be Considered. BUT What you Describe My Experience tells Me Wheel Bearing, It Being a All Wheel Drive Vehicle Makes it Very Difficult to Call This with Confidence as I Am unable to Roadtest it. Hope this Can Help To Lead you in the Right Direction

Posted on Feb 12, 2009

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SOURCE: 1997 Monte Carlo when driving 55-60 motor drops down to 34-40mph

A RESTRICTED FUEL FILTER WILL PROHIBIT PROPER FUEL DELIVERY....CHECK THE FUEL FILTER OR POSSIBLE A WEAK FUEL PUMP...THE ENGINE MAY BE STARVING FOR FUEL AT HIGHER FUEL DEMANDS

Posted on Jan 13, 2009

Rebgagnon
  • 382 Answers

SOURCE: Road Roar

The one thing you did not mention that I needed to do to remove the Hum was 4 wheel alignment. Smooth and quiet now. Hope that helps and have a great day.

Posted on Mar 20, 2009

daves944
  • 1050 Answers

SOURCE: 1999 Harmonic Tone Between 40 and 60MPH

Interesting problem, it always worries me to see new axles and nuts as few mechanics realize how critical bearing preload torque is, and just gun the axle nuts on until they hit the nearest hole on the castle nut. You would not see or hear a single thing with the wheel off the ground either, the bearing needs to be loaded and at speed. Typically though, a bearing noise will be apparent all the time and grow with speed and swerving should have an effect.
From what you say, it does sound like drive line, a bad u-joint to be specific. I'm not that familiar with the Soob's layout, but it must have a driveshaft running from the transaxle to the rear axle. I think if it were me, I would be pulling that shaft out and carefully inspecting it for binding or looseness at any of the joints. 175,000 mi. is a lot and since the other half shafts have likely been replaced, it wouldn't be unreasonable to expect some wear here as well. In fact I think I would probably look around to see if I could just get another center driveshaft with less miles and just put it in to try it. From what you say, this is very likely the cause.
The harmonic balancer is not an issue as you say the noise is independent of engine speed.

BTW. Very good thorough description! I could solve a lot more problems if people were as descriptive as you.

Posted on Mar 30, 2009

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Interesting problem, it always worries me to see new axles and nuts as few mechanics realize how critical bearing preload torque is, and just gun the axle nuts on until they hit the nearest hole on the castle nut. You would not see or hear a single thing with the wheel off the ground either, the bearing needs to be loaded and at speed. Typically though, a bearing noise will be apparent all the time and grow with speed and swerving should have an effect.
From what you say, it does sound like drive line, a bad u-joint to be specific. I'm not that familiar with the Soob's layout, but it must have a driveshaft running from the transaxle to the rear axle. I think if it were me, I would be pulling that shaft out and carefully inspecting it for binding or looseness at any of the joints. 175,000 mi. is a lot and since the other half shafts have likely been replaced, it wouldn't be unreasonable to expect some wear here as well. In fact I think I would probably look around to see if I could just get another center driveshaft with less miles and just put it in to try it. From what you say, this is very likely the cause.
The harmonic balancer is not an issue as you say the noise is independent of engine speed.

BTW. Very good thorough description! I could solve a lot more problems if people were as descriptive as you.

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Road Roar


The one thing you did not mention that I needed to do to remove the Hum was 4 wheel alignment. Smooth and quiet now. Hope that helps and have a great day.

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