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Old 07-09-2005, 05:25 PM   #1
mavx5
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Question Rear Diff Fluid leak - 04 STi

I went to Mr. Tire earlier this week to get a flat tire taken care of, when the tech noticed that the rear diff was leaking fluid. So, I took it to Subaru near my house, and they gave it a look over. They said that "someone" overfilled the reservoir, and it was leaking out.

Now since I don't work on my car, and I do all my maintenances at this Subaru dealership, I'm guessing that they overfilled it during my 15K service.

They said it shouldn't harm anything, but my confidence in them isn't all that high anymore. Does anyone have any thoughts? Does overfilling the rear diff reservoir cause any damage in the short or long term?
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Old 07-10-2005, 01:35 AM   #2
Pakin
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I have a hard time understanding how they may overfill the rear diff. It's near impossible. The rear diff is the easiest fluid change, especially for a dealership since they have the right tools. You don't have to measure how much you need to fill it.

There are two plugs in the back of the case, a top and bottom. All they have to do is drain it from the bottom plug, the tighten the bottom plug back on. And fill the diff from the top plug until it pours out. It just needs to be level with the top plug. It's not bad if it's a bit over the plug, which will drain out after you fill it.

I do not blame you for a lower confidence in them. In fact it's so hard to believe, that I think they might be hiding something.

Here is a pic to give you an idea.



-paK +3
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Old 07-10-2005, 02:50 AM   #3
Vew
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Yeah... I agree with the guy above. You basically fill it until it leaks, let the excess drain, and cap it. Maybe they didn't torqe it correctly or use the Three Bond stuff. It's a liquid gasket you're supposed apply to the threads before recapping it. Kinda expensive, like 15 bucks at the dealership.
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Old 07-10-2005, 04:07 PM   #4
mavx5
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Thanks for the input folks! I think I'll set an appointment with another Subaru dealership in the area and have it checked out.
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Old 07-10-2005, 06:32 PM   #5
ADR 04STi
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Pakin: Thanx for the above instructions. Ill be changing mine very soon.Very handy.
ps: Do you have others? Front Diff & Center. .I could use them too.
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Old 07-11-2005, 01:48 AM   #6
majmun
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The front and center differentials share lubrication with the transmission.
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Old 07-11-2005, 02:36 AM   #7
JPX
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My Legacy's rear diff has been leaking for years. It is coming from the passenger side between the diff body and the seal plate. I had intended to change it when I changed the wheel bearing, but the parts were not available and I needed the car back on the road.

How the hell can anyone overfill that thing? As Pakin's procedure shows, the oil spills out when you reach capacity.
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Old 07-11-2005, 10:39 AM   #8
singletrack
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Quote:
Originally Posted by mavx5
I went to Mr. Tire earlier this week to get a flat tire taken care of, when the tech noticed that the rear diff was leaking fluid. So, I took it to Subaru near my house, and they gave it a look over. They said that "someone" overfilled the reservoir, and it was leaking out.

Now since I don't work on my car, and I do all my maintenances at this Subaru dealership, I'm guessing that they overfilled it during my 15K service.

They said it shouldn't harm anything, but my confidence in them isn't all that high anymore. Does anyone have any thoughts? Does overfilling the rear diff reservoir cause any damage in the short or long term?
Why did they change the oil at 15k miles? The schedule does not call for that...
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Old 07-11-2005, 06:58 PM   #9
mavx5
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I am not sure, that is the "story" they gave me. They probably thought I didn't know better (at the time, I had no idea if they were telling the truth or not). I've already set an appointment with another subaru dealership 10 miles away. Lets see what they have to say...
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Old 07-11-2005, 07:25 PM   #10
eltrouble
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...overfilled the rear differential? wow...it takes skills to do that. You must've had one masterful technician working on your car...

And I don't know about that Three Bond liquid gasket stuff, I simply cleaned off the threads, torqued it down to spec, and I haven't a drop of gear oil from the rear.
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Old 07-11-2005, 09:59 PM   #11
Pakin
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Yes, you don't exactly need any sealant for the drain/fill plugs. They are pipe threads, which are tapered and provide the sealing.

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Old 07-25-2005, 05:49 AM   #12
Blue_Diamond
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one thing you can do is clean the oil off the rear diff and see if it comes back... i had a prob with mine also and subaru said that the guy who filled the rear diff prob forgot to wipe off the excess... but i already checked that by wiping and cleaning it so that i couldn;t see any oil... but then it came back so it had to be leaking...
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Old 07-26-2005, 09:08 PM   #13
sjrhee
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Wierd...I thought rear diffs are a sealed unit? Where would it leak from? if it's from the drain/fill plug area, it could mean the bolt was cross threaded.
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Old 07-28-2007, 08:47 PM   #14
20swrt
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Default overfill differential

Actually, its very easy to go beyond 0.8 quarts when filling up the differential. I actually just overfilled mine - and im a newbie. My driveway is slightly inclined. So when I filled it up - i consumed about 1.2 quarts. I guess overfilling rarely happens at dealerships coz they have lifts.

So experts - let me know how bad is this. Even with normal levels - part of the gear is immersed in oil which in turn lubricates the rest of the differential. This is unlike our engines where overfilling actually causes slushing/foaming which is bad when crank is splashing the oil around.
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Old 08-04-2007, 12:54 AM   #15
proletariandan
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There's no way its going to spill out if it is a little overfilled. There is a vent at the very top of the axle cover but it is WAY above any amount you could get in through the fill hole. My rear diff was leaking on the car I just bought and on closer inspection I found out that the rear axle cover was cracked from the drain hole to the bottom where it seals against the axle/differential housing. The previous owner or whoever he had change his fluid clearly tightened the bolts too much as the recommended torque is something like 35ft/lbs and I had to use my foot on a large ratchet to get both plugs out. I probably could have just HondaBond'ed the crack but I decided to play it safe and replace the cover/gasket and thanks to that decision my car has been on ramps/jacks for more than a week waiting for a gasket
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Old 09-06-2007, 01:40 AM   #16
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Nice Info guys Thanks!
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