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Differential fluid change


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22 replies to this topic

#1 Dennis Methvin

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Posted 07 March 2011 - 01:35 AM

I am getting ready to move from Oregon to Arizona, and i want to change the diff. fluid in my car before i go. The model is a '98 Impreza Outback Sport 2.2L, with a manual transmission.

1. Does this model contain drain plugs that allows me to easily change it on my own? I want to do both front and back.

2. What kind of fluid does this model take? fully synthetic? Do they recommend a certain brand and such?

3. I do all the maintenance on my car, but if this is going to be a huge process, would taking the car to Oil Can Henry's to get this done suffice?

I would really appreciate any insight on this. Thank you!

Dennis

#2 GLCraig

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Posted 07 March 2011 - 02:09 AM

1. Yes. The rear diff is pretty easy to get to. The transmission and front diff share a common drain plug. You will need to jack yup the car to get to it. Unless you are really skinny and have long arms.

2. Pretty much any 75w90 GL5 will work. My preference is Redline 75w90 NS, this is not the same as their regular 75w90. The 75w90 NS dose not include the additive for limited slip diffs. Without the additive, the syncros in your transmission will work better.

3. If you have the tools, go do it yourself.

As for you trip to Arizona, this is route I've taken in the past.
http://maps.google.c...4,26.784668&z=6

#3 Olnick

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Posted 07 March 2011 - 03:54 AM

+1 what GLCraig said. Front is as easy as draining crankcase oil. You will need a small funnel since you have to refill through the tranny dipstick tube.

Rear diff has two screw-in plugs, one above the other. They will be very, very tight! Half-inch drive breaker bar fits perfectly but you will probably need an extender. Make sure you remove the TOP plug first!

#4 Suzam

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Posted 07 March 2011 - 10:11 PM

+1 on the top plug first. You don't want to pull the bottom and drain the oil out and not be able to refill it because you can't remove the top one!

#5 rverdoold

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Posted 08 March 2011 - 01:50 AM

Also do not forget the clean the magnet in the drainplug bolt. This will contain shavings from teethwear. You can also try a bit to clean inside the drainplug hole with a fiberfree cloth.
I have 70w95 synpower from mobil i thought

#6 charm

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Posted 07 April 2011 - 05:30 PM

The 1/2 drive felt a little loose in the square plug. Y'all sure it won't strip it?

Just double checking.

#7 1-3-2-4

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Posted 07 April 2011 - 06:22 PM

trust me it will turn I use a 1/2" 18" breaker bar (I have air tools now) and while it feels loose it will be fine and wont strip.

As for filling the rear you can be creative.. I've just poured the bottle in until it started to pour out of the top hole.. OR you can get tired of that and buy a push pump that screws on the bottle :)

#8 charm

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Posted 07 April 2011 - 06:41 PM

All right! I'll put my back into it (and a little PB Blaster) tomorrow. The front diff went well enough, the rear, once those two plugs come out, should be easy as well.

trust me it will turn I use a 1/2" 18" breaker bar (I have air tools now) and while it feels loose it will be fine and wont strip.

As for filling the rear you can be creative.. I've just poured the bottle in until it started to pour out of the top hole.. OR you can get tired of that and buy a push pump that screws on the bottle :)



#9 1-3-2-4

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Posted 07 April 2011 - 06:53 PM

yeah try using some Pb blaster and if that does not work I've used my feet and I've used a jack to help break it loose.

#10 bpearson

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Posted 07 April 2011 - 06:57 PM

Just a thought>>>>>
If its been a long while since its been changed, what I've done is once the rear diff is drianed I use a can or carb cleaner with the straw attachment and stick it in the top hole and blast out any junk and metal shavings that could still be stuck in there. There is some nasty looking black crud that comes pooring out and it helps to clean the metal surfaces so the new oil has a better ability to penetrate/protect... Its worked good for me.

Wouln't recomend this for the front diff though, not sure what effect it would have, could be harmless but I haven't done it....

#11 charm

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Posted 07 April 2011 - 07:02 PM

On an auto, like mine, it shouldn't matter.

The recommended interval is 30k miles. Most people double that, at least. I've owned the car for about 60k miles and who knows how long it's been since it was changed before that.

It's not that hard or time consuming to do. I may just do another change of gear oil in a few months and call the oil I'm putting in right now the cleaning oil. I'll let the clean stuff really work its way through everything and get all the goo. I'll let it carry all those little metal shavings to the magnet. Then, whamoo, I'll change the fluid again creating a nice clean gearbox.

At somepoint I'll do the tranny too. I may just pay to have it flushed instead of drain, refill, drain, refill, drain, refill. Seems like such a waste of ATF.


Just a thought>>>>>
If its been a long while since its been changed, what I've done is once the rear diff is drianed I use a can or carb cleaner with the straw attachment and stick it in the top hole and blast out any junk and metal shavings that could still be stuck in there. There is some nasty looking black crud that comes pooring out and it helps to clean the metal surfaces so the new oil has a better ability to penetrate/protect... Its worked good for me.

Wouln't recomend this for the front diff though, not sure what effect it would have, could be harmless but I haven't done it....



#12 johnceggleston

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Posted 07 April 2011 - 07:04 PM

2 things:
1. remove the FILL PLUG FIRST. you do not want to drain the rear diff only to learn you can't refill it.

2. i used a bent penny to make the 1/2" drive fit a little tighter. you probably don't need to but it works pretty well. just bend a penny in to a 90* angle. i used my vice and a hammer. but big pliers and a hammer should work too.

i love ''free'' tools, well $.01 tools any way. :lol:

#13 Fuzpile

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Posted 07 April 2011 - 09:31 PM

I merely add that I was unfamiliar with these cars yet determined to replace all fluids. From every effort there was improvement. The rear fill plug was particularly difficult. Tellin you that electric impact didn't move it and 1/2" pneumatic wouldn't either. These are facts. I finally had my 3/4" with about 100 psi working thru 2 or 3 extensions. And it still wouldn'e come loose. The extension absorbed the impact so I had to get under there and directly apply this 3/4" to the plug, then it released.
The 1997 oil or what was left of it was replaced:)

#14 Fuzpile

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Posted 07 April 2011 - 09:44 PM

It's a known fact that there was an adaptor involved. Didn't seem worth mentioning. It was a Thorsen and I fully expected it would shear but it didn't.

#15 Fuzpile

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Posted 08 April 2011 - 03:34 AM

Dang, I just have to say something. John touched it and it's a raw nerve about pounding what becomes copper into the spaces>Spaces between. This is important to consider especially when dealing with taps, not-so easy outs and stuff. that is if the driver actually Deforms the plug and expands it while removing.... then we have a different situation. again jC made a good point in that the torque must be contained to the issue.

#16 987687

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Posted 08 April 2011 - 06:14 AM

I couldn't get the drain plugs out of the rear diff with my breaker bar... I couldn't exert enough force. I eventually used the spare tire jack to push the breaker bar up. That eventually cracked them loose.

I found that I could squeeze about 1/3 of a bottle into the top hole before I couldn't tip it high enough to get any more out. This is fine as long as you do the diff before the transmission. Then just put the partial bottles in the tranny.

funnel makes it easier, but you don't HAVE to have one to fill the tranny. Gear oil bottles have the little spout so you can get it in there.

#17 1-3-2-4

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Posted 08 April 2011 - 08:07 AM

Ive filled the front without a funnel but better have good aim

#18 greenleg88

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Posted 03 May 2011 - 03:30 AM

I found that I could squeeze about 1/3 of a bottle into the top hole before I couldn't tip it high enough to get any more out. This is fine as long as you do the diff before the transmission. Then just put the partial bottles in the tranny.

funnel makes it easier, but you don't HAVE to have one to fill the tranny. Gear oil bottles have the little spout so you can get it in there.



i think im a little confused by this ^. that sounds like the rear diff is connected to the front tranny fluid? is that what youre saying? (i dont know how it all flows... or if theres hoses that run back and forth.. i would have thought the rear diff and front diff are completely independent...)

#19 987687

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Posted 03 May 2011 - 05:51 AM

They're separate. What I'm saying is that without an oil pump it's difficult to fill the rear diff. But if you get the bottles of gear oil with the nozzle thing at the top you can get about 1/3 of the bottle into the rear diff without too much trouble.
The diff only holds about 1qt. So if you use 1/3 of three bottles in the diff it's full. Then you have 3 bottles 2/3 full, dump those in the tranny.

If you fill the tranny first and leave just one bottle to fill the rear diff you have to get creative

#20 1-3-2-4

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Posted 03 May 2011 - 03:31 PM

I just did mine last friday

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#21 Olnick

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Posted 03 May 2011 - 03:52 PM

I couldn't get the drain plugs out of the rear diff with my breaker bar... I couldn't exert enough force. I eventually used the spare tire jack to push the breaker bar up. That eventually cracked them loose.

I found that I could squeeze about 1/3 of a bottle into the top hole before I couldn't tip it high enough to get any more out. This is fine as long as you do the diff before the transmission. Then just put the partial bottles in the tranny.

funnel makes it easier, but you don't HAVE to have one to fill the tranny. Gear oil bottles have the little spout so you can get it in there.



Excellent suggestions. I too used the car's scissors jack to break the drain plugs loose.

To refill the rear diff I ran a small plastic tube from the fill hole, out through the passenger side wheel well and attached it to a funnel. Mounted the funnel high enough to let gravity do its thing--slow but effective!

#22 Suba9792

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Posted 03 May 2011 - 04:01 PM

ok I may have failed to notice but is this for a MT or a 4EAT?

#23 SnatchedHatch

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Posted 09 November 2014 - 06:21 PM



Excellent suggestions. I too used the car's scissors jack to break the drain plugs loose.

To refill the rear diff I ran a small plastic tube from the fill hole, out through the passenger side wheel well and attached it to a funnel. Mounted the funnel high enough to let gravity do its thing--slow but effective!


This whole thread is exactly what I needed, excellent tips!

I have a '98 Subaru Outback Sport auto,
planning to do this soon.

Tips I've taken:
1. Fill plug pulled first.
1.A. Use bent penny or copper to facilitate the removal of the plug without an adapter.
2. Pull drain plug and clean the magnet on it.
2A. If desired, clean out the diff using "carb cleaner". Seafoam spray should work, they make a pour-out version for diffs and trans.
3. Buy hand pump if cheap, or use tube and funnel to refill diff after replacing the drain plug, due to the tight space above the fill plug.
4. (Replace Fill Plug of course).

75W90,
I've heard Royal Purple synthetic is good, any other types recommended?

I should steer clear of gear oil meant for use in limited slip differentials, due to the additives that can reduce performance in the OBS diff. Thanks to GLCraig for that tip^^

Edited by SnatchedHatch, 09 November 2014 - 07:36 PM.





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