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2004 Forester XT
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64 Posts
Discussion Starter · #1 ·
Does anyone else's rear diff weep?

I'll grab some photos this evening if its not raining and update this post, but I noticed on the weekend my rear diff seems to be weeping more than I would like it to.

My flat mate, who has a long history of working on Jeeps and other domestic 4x4's, mentioned that all diffs he'd ever worked on weeped a little and that it was nothing to worry about.

Anyone got $0.02?
 

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04 Forester X, MT
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1,039 Posts
Subarus hold less than 1 qt of oil in the diff, so there's not a lot to lose. Most Jeeps and domestic 4 x 4s would hold 2 qts +.

As things get older they will leak. Does it leak enough to drip where you park it or is it blown on other parts besides the diff? I think that would be too much, especially if you drive it a lot.

Tighten the plug if it's leaking there, that would be easy to do. Otherwise, it's axle seals, pinion seal, or diff cover sealant to repair at some point. If it's a local beater car you don't want to spend money on or you don't put many miles on it you could leave it awhile with a minor leak and check occasionally. If it's newer or your main transportation then I would tend to fix sooner rather than later.

I've had Foresters at 90,000, 120,000, and 135,000 mi and none of them leaked at the rear diff. Sadly, they are more likely to lose headgaskets!

I did have an Outback/Legacy loaner once with 225,000 that did have rear diff leak that I pointed out as marginal and likely needing fixed when I returned it. I believe I noticed a few drips maybe the size of dimes on the garage floor after having for a few days where it would be parked overnight.
 

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1998 Forester
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213 Posts
First make sure that is not over filled. I have seen them leak from the pinion seal and the cover gasket. Mine is leaking from the rear cover just need the time to take it apart.
 

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2004 Forester XT
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64 Posts
Discussion Starter · #4 ·
I had the pinion seal replaced 2500kms ago. I guess it could have been overfilled at that time. I'll inspect closer, clean up the residue and monitor it closely after a good clean up. Is there any way other than drain and refill to ensure it is not overfilled?
 

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1998 Forester
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213 Posts
The level should be just below the fill plug hole. Just pull the fill plug and see if anything comes out if oil comes out it is overfilled.
 

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04 Forester X, MT
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The preferred oil to use to refill an 04 XT Subaru rear diff would be?
I used standard 80W90 on my X the first time I changed it (manual says you can). It was noisy. I then went to mobil 1 75w90 synthetic with LS additive and put a 1/2 tube of extra LS additive in for good measure. It sure runs a lot quieter. I plan on using Castrol 75w90 synthetic next time to see if any different.

If you have an MT don't use any diff oil with LS on it unless it specifically says for Manual Transmissions. Some have said it makes for bad shifting and/or tranny damage. I found this synthetic 75w90 Lubro-Moly that Napa can order (made in Germany, comes in 1 L bottles) and I have been using that in my MT and been very pleased. Good shift feel and especially better in cold weather.
 

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2004 Forester XT
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64 Posts
Discussion Starter · #9 ·
What is LS additive?

Google-ing LS as an acronym doesn't give me anything obviously transmission related.
 

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04 Forester X, MT
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What is LS additive?

Google-ing LS as an acronym doesn't give me anything obviously transmission related.
I think I bought this at advance or autozone. I think it helped noise a little.

 
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