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2005 Impreza- rear differential noise?


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My mechanic confirmed the whine I'm hearing at highway speeds is due to bad bearings in the rear differential. The car is an 2005 Impreza Outback Sport, automatic transmission with 253K miles. He recommended getting a used one if I can find it for a good price. I see several on Ebay shipped for $200ish. They are advertising that this car has a 4.11 gear ration, bur I tend to take Ebay car specifications with a grain of salt.

Can anyone confirm that the correct gear ratio for this vehicle is 4.11?

 

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The basic symptoms are a whine at higher speeds but only in AWD. In FWD when not under load it is much quieter. Also,  there is no difference in noise in turns, so not thinking rear wheel bearings. My mechanic was able to remove the stripped differential plugs and found the oil was pretty nasty and seemed thin.

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I agree probably not the diff. Run it on the lift and stethoscope the diff and bearings. This is very easy to determine with 100% accuracy. 

I would also guess wheel bearings. I have replaced diffs..... maybe half a dozen over the years. I've done hundreds of wheel bearings. It's probably 100:1 bearings vs. diffs. And the diffs I have replaced are usually run dry or are one of the weird ratio VLSD models that like to eat themselves. Extremely rare. 

Rear wheel bearing usually don't respond to steering input. 

GD

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Thank you. I was also chatting with my mechanic about a vibration that can be felt when accelerating. It can be felt throughout the whole car and when I had the car in FWD to check the rear end noise, the vibration was noticeably worse. There isn't any noticeable vibration running at highway speed.

I know the front CV joints are likely shot (after buying the car, I noticed both front axles are original with split inner boots and have thrown quite a bit of grease) and new axles are next on the list. I'm thinking maybe worn CV joints and the vibration was worse because all of the torque was going to the front wheels when in FWD? I also noticed a bit of noise coming from the front of the car in addition to the intermittent whine from the back. 

Any other possible causes for the vibration under acceleration?

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  • 6 months later...

As a follow up, the vibration I felt on acceleration went away when the new front axles were installed (the old ones had flung a lot of grease out of the inner CV joints). The whine from the rear still persists but practically disappears when in front wheel drive only. I also get a slight vibration at highway speed that doesn't vary on turns or whether in FWD or AWD. Wonder if both symptoms could be wheel bearings, and if so, how to check to be sure (since they are pricey for my mechanic to replace).

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8 hours ago, Stevo F said:

As a follow up, the vibration I felt on acceleration went away when the new front axles were installed (the old ones had flung a lot of grease out of the inner CV joints). The whine from the rear still persists but practically disappears when in front wheel drive only. I also get a slight vibration at highway speed that doesn't vary on turns or whether in FWD or AWD. Wonder if both symptoms could be wheel bearings, and if so, how to check to be sure (since they are pricey for my mechanic to replace).

Check carrier bearings, ujoints and rear wheel bearings.  

If someone with decent hearing sits in the back the wheel bearing should obviously be from one side or the other. 
 

bearing noise it one corner, diff or shaft will be central   

or wait - wheel bearings slowly get worse over time.  Eventually they start to get worse quickly.  Then you’ll know for sure. 

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1 hour ago, Stevo F said:

it started the same day I had new tires put on the car. Eliminated it being tire noise itself

Huh? Something was changed, and something changed, so they clearly can't be related? What kind of tires were put on? Are they all the exact same?

 

 

When I was at the dealership, we bought a 4.11 Subaru diff from a junkyard for a customer car, and it ended up being wrong (I think it was like a 2010 Legacy MT that used different axle splines). He said they usually throw away the common 4.11 diffs, and it wasn't worth the cost to ship it back to him. I still have it...just in case....

What I'm saying is. A. It's very unlikely that it's your problem unless the fluid has leaked out B. You should be able to get one cheap. Don't look on ebay, as shipping will kill you. www.Car-part.com and you can find one at a local yard for much cheaper.

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9 hours ago, Stevo F said:

Tires were all a brand new matched set. I tried swapping in a spare for each tire and have rotated them with no change. We changed the diff fluid after this started with no change

LOL, changing one tire out is not going to make enough of a difference to really come to any decent conclusion.. change out all 4 and see if there is any difference. That would be MUCH more conclusive than swapping one around the car.

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On 2/4/2020 at 7:34 PM, heartless said:

LOL, changing one tire out is not going to make enough of a difference to really come to any decent conclusion.. change out all 4 and see if there is any difference. That would be MUCH more conclusive than swapping one around the car.

That's a good point. I'm thinking of swapping all 4 wheels from my smooth riding Legacy (same size tires) and seeing how each vehicle drives afterwards.

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  • Stevo F changed the title to 2005 Impreza- rear differential noise?

I did swap tires with the Legacy and there was no change in the noise, so I've confirmed it's not the tires.

While I was test driving, I did take a video where you can hear the higher whining noise in the background. Please take a listen and let me know what you think.

 

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