('14+) Observations on my first Front and Rear Differential Fluid Replacment - Subaru Forester Owners Forum
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post #1 of 26 (permalink) Old 01-15-2017, 03:51 PM Thread Starter
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Observations on my first Front and Rear Differential Fluid Replacment

I recently passed 30K miles on 2016 2.5i Premium. So I drained and refilled the Front and Rear Differential fluid today, and thought I would document my journey and add some observations that might be helpful to other noobs like me!

First, I have the FSM for my car, so I carefully studied the manual and read up on the wonderful how-to threads in this forum. Thank you to everyone that posted, it was very helpful!

Here is the gear oil I used from wally-world. It is GL5 and meets the specs in the manual:



Rear Differential

I lifted up the car and placed it on four jack stands. This gave me enough room to to get my breaker bar on the plugs. Without the car being lifted on jack stands, I didn't have enough room to turn the breaker bar. The fill and drain plugs are clearly marked with a yellow dot. The top plug is the fill and the bottom is the drain.



Both plugs are a 10mm hex socket and I had to use a 3/8 inch breaker bar to break them free.



The oil that drained out of the rear differential was a disgusting looking grey fluid. It looked very dirty. The drain plug has a magnet to catch the metal sludge. Here are the plugs before cleaning them:



I cleaned up the plugs and replaced both gaskets per the FSM recommendation.



I replaced the drain plug and tightened to spec - 36.9 ft lbs.



To refill with new gear oil, I rigged up some tubing to the spout of the bottle. The tubing had a tendency to come off the spout, so I had to add a zip tie to hold it on tighter. Luckily, there is a small ridge that goes around the spout of the bottle that I could use to hold the zip tie.



I fed the end of the tube into the filler hole and squeezed the bottle to feed the oil into the differential. It worked quite well, with minimal spilling. It took nearly the entire quart bottle, although the specs call for 0.8 quarts. I did lose a little from the hose, so I think this is why I used nearly the entire bottle. Once I started getting a small stream from the fill hole, I closed up the filler plug, tightened it to spec and moved on to front differential.

Front Differential

The front differential is little more challenging to get to. First, I pulled off the front passenger side tire so I could get to the fill plug.



I read and took the advice of those before me to check and make sure that you can break the fill plug free before draining the old oil out! This would have been much easier if I had an extension set for my breaker bar. You need a good set of extensions because there isn't much room to play around in there. Luckily for me, I was able to get my breaker bar in behind the exhaust and break the fill plug free. This was an 8mm hex socket.



Next, you have to remove the front under cover - transmission in order to gain access to the overflow plug and the drain plug. There are 5 screws and 2 clips to take out. I had to print the page from the FSM and bring it with me to figure it out since it was my first time. Here is pick of the under cover directly below where it sits on the car. This is a view from the front drivers side.



With the front under cover - transmission removed, you have easy access to the overflow and drain plug. The overflow plug was an 8mm hex and the drain plug is a 70 Torx. The Torx Drain Plug is clearly marked as Diff Oil.



When the oil drained out, it didn't look bad at all. It had a nice golden color to it still. This was much different than the oil that drained from the rear. The front drain plug also has a magnet to catch the metal sludge.



I cleaned it out and replaced the gasket. This gasket is a different part number than all the others.



After draining the oil and cleaning the plug, I replaced the drain plug and tightened it to spec - 51.6 ft lbs. I left the overflow unplugged because you need to fill the differential until there is a small stream from the overflow plug. This part was pretty straight forward. I filled the front differential using the same vinyl hose setup as the rear differential. It took between 1.4 and 1.5 quarts, exactly according to the specs. It was much easier to fill the front as my hose was long enough to reach into the fill hole and still allow me to hold the bottle up and squeeze the oil out.

Finally, I closed up the overflow plug and the fill plug. I couldn't get my torque wrench onto the fill plug because there wasn't enough room, so I tightened it as much as I could with my ratchet.

Observations

First, it was very easy once you have it figured out. The hardest part is getting started! I would recommend having a good set of hex sockets (10mm and 8mm) and a T70 Torx bit.

Very helpful would be an extension set that fits your hex socket set. This would be especially helpful with the front differential fill plug. You need about 20 or 24 inches of extensions to reach that plug. Torque wrench is a must!

The rear diff oil was disgusting and I should have changed it much earlier. So if your wondering if you should change it early, I say go for it. The rear is very easy to do. The front diff oil still looked good and I'm glad I changed it out before it got too bad. I will probably drain and replace the diff oil every year as a routine maintenance item.

Finally, the FSM is extremely easy to download from the Subaru Technical Information site. A three day subscription only costs $35 and you can download the entire manual plus additional training documents. I would highly recommend it.

Hope this helps someone!

StanF.

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Last edited by StanF; 01-17-2017 at 01:10 PM. Reason: fixed typo error for 3/8th inch breaker bar
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post #2 of 26 (permalink) Old 01-16-2017, 05:14 PM
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Nice informative write up! Thanks for sharing.



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post #3 of 26 (permalink) Old 01-16-2017, 05:43 PM
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why did you go with that gear oil, isn't supertech the "cheap" stuff?
just wondering, im getting ready to do this too.thx
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post #4 of 26 (permalink) Old 01-16-2017, 05:43 PM
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Very nice write up. The pics you added are fantastic.

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post #5 of 26 (permalink) Old 01-16-2017, 05:49 PM
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Yes thank you for sharing your job w/pics. I will be doing my rear diff this summer on my '15 2.5i when I'm hitting 3 years. Only have 12k miles but follow the severe service maint. schedule due to my driving conditions. Rear diff seems doable for me from the ground without jacks, front diff more than I want to deal with I'll have my independent Sube shop do it.
FYI for doing both diffs my Seattle area Subaru shop wants $172 complete incl. shop supplies and tax. That's actually on the low end for this service in my area I've found out...

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Last edited by kōbai-iro; 01-19-2017 at 03:50 PM.
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post #6 of 26 (permalink) Old 01-16-2017, 06:18 PM
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Good write up!

As a reminder for some people, the XT model has a different style front differential. You can see how to fill it here: How To: Front and Rear Differential Oil Change - 2014 FXT CVT

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post #7 of 26 (permalink) Old 01-17-2017, 01:34 AM
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Thanks...subbed to thread.

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post #8 of 26 (permalink) Old 01-17-2017, 01:34 PM Thread Starter
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Quote:
Originally Posted by Thegreatdognate View Post
why did you go with that gear oil, isn't supertech the "cheap" stuff?
just wondering, im getting ready to do this too.thx
I had really had to think about my motivations for buying that particular gear oil before answering this question. Generally, when it comes to my Subaru, I'm not that focused on cost. I like to purchase OEM parts from a dealer so that I am confident that I am getting original parts, even though I know it costs a little more. But, I don't really think this way when purchasing fluids like motor oil, gear oil, brake fluid, washer fluid, etc. As long as the fluid I'm getting meets the specs in the manual, I'm fine with it.

So, I always buy my motor oil (Pennzoil Platinum 0w-20 full synthetic) at Wally-World because it's cheaper. I went there first to see what kind of gear oil they had. Super Tech was the only one they had that was 75W-90. They had other brands, and some that were full synthetic, but they were 80w-140 which is not the spec for my car.

When it comes to Super Tech, I consider it equivalent to other store brands. In other words, its no different buying Super Tech or AutoZone or Advanced Auto brand oil. Wal-Mart doesn't make the oil, they buy it from a refiner and resell it in their stores. As long as it meets the SAE grade and GL-5 spec for my Forester, I'm confident that it will work fine.

And, I plan on replacing the diff fluid every year because I put about 25K to 30K miles a year on my car. I couldn't justify paying $10 or $20 per quart for name brand stuff if I'm going to dump it out (I mean recycle!! ) and replace it again next year.

Sorry for the long winded answer, but hopefully it helps explain my thought process on SuperTech oil.

StanF.
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post #9 of 26 (permalink) Old 01-17-2017, 02:16 PM
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Do you notice any performance difference, i.e., the way the CVT shifts ... or doesn't shift? ;)

Since yours was that dirty I'm thinking I should probably get mine changed at next service. The dealer recommends changing at 30K, but I wasn't sure that was just a money-making recommendation or something that's really needed, since it's not in the maintenance schedule (except for severe service). Sounds like it might be a need, perhaps low priority.
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post #10 of 26 (permalink) Old 01-23-2017, 07:04 PM Thread Starter
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Quote:
Originally Posted by RocketDawg View Post
Do you notice any performance difference, i.e., the way the CVT shifts ... or doesn't shift? ;)

Since yours was that dirty I'm thinking I should probably get mine changed at next service. The dealer recommends changing at 30K, but I wasn't sure that was just a money-making recommendation or something that's really needed, since it's not in the maintenance schedule (except for severe service). Sounds like it might be a need, perhaps low priority.
I didn't notice any performance difference after the change. However, I would really emphasize that the rear differential oil was VERY dirty. If you are in doubt, I would say that you should change the rear diff at 30k at a minimum. It's very easy to do it yourself.

If you plan to take it to your dealer, ask if they'll give you a discount if you do both front and rear at the same time. My dealer said they would do both for $169, but I don't know if this included the price of the Subaru gear oil. I did mine for about $40 for the oil and replacement washers.

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post #11 of 26 (permalink) Old 01-24-2017, 03:20 AM
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Question Stan,
Are the oem diff plugs magnetic ?
If not Im going to order Dimple Plugs for mine before I do it.


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post #12 of 26 (permalink) Old 01-24-2017, 03:48 AM
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@DockingPilot - If I remember right, on mine the front was but the rear was not.

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post #13 of 26 (permalink) Old 01-24-2017, 04:15 AM
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Ok, thanks Josh.


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post #14 of 26 (permalink) Old 01-24-2017, 09:36 AM Thread Starter
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Quote:
Originally Posted by DockingPilot View Post
Question Stan,
Are the oem diff plugs magnetic ?
If not Im going to order Dimple Plugs for mine before I do it.
Both of the drain plugs were magnetic. I have pics in my original post.

StanF
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post #15 of 26 (permalink) Old 01-24-2017, 09:39 AM
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Supertech is good gear oil. I use it in my manual trans and it shifts good, and is only about $5 a quart.
I replaced my rear dif oil at 10,000 with Supertech and it was really dirty like your pics.
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