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Noise from rear - wheel bearing or differential ?


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Hello - new to this forum - all looks good so far.

Need some advice please: 

2007 2.5 SE manual outback making a real werring noise from the back (my wife describes its as having a motor bike behind you the whole time).  Starts in around 30mph the gets louder as you go faster and its slowly getting worse. So far I have tried:

1. Checking the centre bearing on the prop shaft: Turns freely - not that

2. Changing the passenger side rear wheel bearing (hub assembly) - where the it sounded like it was coming from if you sat in the back - not that.

Now wondering if it is

A. Other rear wheel bearing,

B. one of the drive shaft joints (unlikely - all 4 CV rubber boots like fine) or

C. The differential.

 Tempted just to swap out the diff. as a precaution BUT not sure if the many diffs from gen 3 outback diesels listed on eBay are correct for this 2.5 SE manual.Is there a listing anywhere for diff. part numbers to model / year?  Is there a fool proof way of sorting out a noisy differential form a failing wheel bearing ?

Don't want to start a 'money pit' round of swapping out parts needlessly but do need to get this fixed. So any advice or guidance would be much appreciated.

PS: Generally well impressed by the elegance of the design of these cars. 


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Couple ways test this,

I put vehicle on lift and run it in air and listen at hubs etc with stethoscope

You can also tell a lot if experienced from road test by how noise changes as come on off throttle (wheel bearing stays same besides speed of noise while a diff changes drastically as power comes on and off
Also rocking steering left to right will load bearing and change/stop noise indicating bearing and what side .

If you got axles stands and flat ground you could try run it while on 4 stands for a good diagnosis .

It would take me 15minutes check that out so maybe worth going to decent garage and get them check it vs the part cannon method .

If you gambling man do the other bearing (bearings are common on these)

Use decent brand bearings/hubs (preferably japanese) as the cheap euro stuff pretty poor and can soon be bad again or bad straight out the box .

Also worth checking/draining the diff oil for inspection if got any doubt on it .

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Many thanks.

Will chance it on the other bearing first before going for the differential. Kicking myself for fitting a cheep bearing first go - should know better. Now have a good one (!Removed! brand) on order to fit in at the weekend. Hoping that will do it.  Aiming for a sub 3hr job having done the learning on the passenger side. Will do a soak with 3in 1 penetrating spray on the bolts a couple of days before.

Re differential specs - is it safe to assume that a rear diff. from a gen 3 outback Diesel will fit a gen 3 (up to 2009) petrol ?  Guessing that the gear box ratios would be different but final drive ratios would be the same to variety and costs down. 

BTW - clicked the XV forum for this for some reason - this should be under Outback.



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  • 2 weeks later...

Update on how things went.

In short - it was the other rear wheel bearing - as well !  They were both on their way and noisy, just the drivers side was noisier (further gone) ..but I changed the passenger side first. Hmmm.

In detail

Noise from rear end started around 109.5K miles, Vibration first kicked in when doing 60mph plus.  Over about 400 miles this came down to 20mph. After much listening and checking went for the passenger side rear wheel bearing. Once off this felt tighter to turn than the new unit - so I thought that was it. Wrong - noise almost as bad. Then came on this forum for much needed advice.

Got a quality replacement rear hub / bearing assembly (eventually - now disenchanted with eBay spare parts suppliers - another story)  and fitted that on the drivers side. Noise gone - back to normal - relief. The one taken off was very tight compared to the new one - well on its way to full seize up.

On reflection: Its probably really hard to tell which side bearing is failing because the entire rear transmission and suspension is mounted on a sub frame. So the path for the vibration into the body structure is different from a lot of other vehicles - it just sounds a lot different.  The advice on the side of the spare part box 'change both sides' is good - if you can afford it. Chances are if one side is on its way, the other will follow sometime soon.  

Generally, as a DIY mechanic with 30 year experience well impressed with the engineering on this car: Great design and very doable ... if you have the right tools ;-).


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