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Old 06-23-2008, 12:10 PM   #1 (permalink)
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Default Change out your rear differential fluid now!

After only 23,000 miles I had lots of shavings and a square chunk of metal the size of a BB clustered around the magnet. The dino oil looked trashed too. I know I probably wouldn't have had this much wear and tear if I had switched to Motul 300 synthetic in the beginning.

So what causes heavy wear in the rear differntial? It's not like I am enaging it manually like the transmission....replaced that with Motul 300 too because it it looked like tea. I'm thinking 20K intervals should be about right for the rear differential but I'm thinking 30K for the transmission. Shifts like a drream now!

Last edited by forest_explorer; 06-23-2008 at 01:39 PM.
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Old 06-23-2008, 01:14 PM   #2 (permalink)
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Changed mine not long ago and have 120000miles on mine. Looked really good and owned the car for 3 years now.

I would have went to the dealer with that. It doesn't seem normal to have huge chunks.
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Old 06-23-2008, 01:23 PM   #3 (permalink)
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If you found chunks, you may want to tell the dealer about it. I had my rear diff replaced by warranty. It blew up while driving, and I have pieces of it from when they took it out.
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Old 06-23-2008, 01:24 PM   #4 (permalink)
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Originally Posted by huck_this View Post
Changed mine not long ago and have 120000miles on mine. Looked really good and owned the car for 3 years now.

I would have went to the dealer with that. It doesn't seem normal to have huge chunks.
I wouldn't call BB-sized huge.... I think I will tell my Subaru dealer about it just in case something happens later but I think I'll probably be OK with Motul 300 oil being changed out every 20K.

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Old 06-23-2008, 03:53 PM   #5 (permalink)
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I've heard stories like this before. How about the front differential fluid?
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Old 06-23-2008, 04:02 PM   #6 (permalink)
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The front is not nearly as critical. When I first did mine the front looked like new compared to the rear diff fluid.
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Last edited by SuperRu; 06-23-2008 at 04:18 PM. Reason: spilling
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Old 06-23-2008, 04:15 PM   #7 (permalink)
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I changed out mine at 12,000 miles and daughters at 14,000 miles.
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Old 11-26-2008, 10:53 PM   #8 (permalink)
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Update--I just changed my rear differential fluid again. It had only been in for 8,000 miles(31K total) and this time there was just a little bit of black muck on the magnet(probably leftovers coating the housing from before) and the oil itself looked like it just came out of the bottle. I'll give Motul all the credit for this happy ending.
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Old 11-27-2008, 03:38 AM   #9 (permalink)
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Originally Posted by forest_explorer View Post
I'll give Motul all the credit for this happy ending.
I doubt that that has anything to do with it. My initial change was very clean and my second change with Mobil 1 was clear as a bell. You just had a lotof crap in there from the factory and it discolored the oil.

But the good news is that things look good and you have no noise (I assume). Certainly not knocking Motul.its as good as it gets.
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Old 11-27-2008, 07:41 AM   #10 (permalink)
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I just put in some Mobil 1 75/90 LS a week ago. I had the non-LS 75/90 in there before for 20K. The magnet was grey, but very little shavings compared to the first change after the first 25K.
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Old 11-27-2008, 09:59 AM   #11 (permalink)
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Quote:
Originally Posted by adc View Post
I doubt that that has anything to do with it. My initial change was very clean and my second change with Mobil 1 was clear as a bell. You just had a lotof crap in there from the factory and it discolored the oil.

But the good news is that things look good and you have no noise (I assume). Certainly not knocking Motul.its as good as it gets.
Uh, there was enough shavings and chunks in there with the dino oil to make a dime out it....not normal if you ask me. I'm just glad it looks like I'm not going to be needing a new differential anytime soon after all.
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Old 09-09-2009, 12:26 PM   #12 (permalink)
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I just changed the differential oils on my 2008 AT with 13,000 miles. I had collected various posts on how to do it, and noted these items of interest:

1. It was not particularly hard to break loose the rear diff plugs. They don't have gaskets, but wedge themselves, so I put a little Hylomar blue gel sealant on the threads. It does not get hard, but will stop seepage.

2. The front diff plug uses a hard thick solid copper gasket. I had bought a $3 new one, but the old one was perfect and could have been reused.

3. Although both diffs use the same gear oil, the rear oil was watery and gray, while the front oil was still light amber and viscous. The rear plug magnet also had a thick coating of black ferrous fuzz, while the front magnet had only a light coating.

4. I replaced the OEM dino oil with Redline synthetic 75W90 GL5 gear oil. This has got to be a "must" for the rear differential, which quickly destroys dino oil. I also wish I had done this much sooner. Subaru really ought to require this as part of the first 7500-mile service.

5. The previous posts said buy 3 quarts because the rear diff takes almost 1 quart and the front diff takes 1.3 quarts. With the car level, I stopped pumping the rear diff as soon as it overflowed, and put the rest of that quart plus another quart into the front diff. The front diff came exactly to the F (full) mark. So 2 quarts fill both differentials if the car is level. If the car is ramped, oil flows to the front of the long rear housing, which will be overfilled when the car is level, and also require buying a 3rd quart for the front differential, of which only a little bit will be used.
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Old 09-09-2009, 12:43 PM   #13 (permalink)
 
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I changed my diff oil at 15K and the rear was super nasty. My buddy who works at our local subie dealership changed his STI's diff oil every 5K and says it looks nasty after 5K miles.
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Old 09-09-2009, 12:46 PM   #14 (permalink)
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I changed the rear diff in both my Foresters around 30k. The XTs magnet was clean, but the fluid had a lot of brown in it. The Xs magnet was covered in shavings and sludge, but the fluid looked pretty good.
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Old 09-09-2009, 01:18 PM   #15 (permalink)
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I think we need to start a photo gallery of transmission chunks...maybe even turn them into avatars or emoticons. I am getting my AT fluid changed and Diffs also next week. At 120K we'll see what they look like.
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