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rear diff oil


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50 replies to this topic

#1 brus brother

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Posted 14 September 2003 - 12:07 PM

Is there any homespun way of opening the drain and fill plug on rear diff on a 90 Loyale or do I have to get a special tool? It is an internal square on the plug.

#2 ScoobySchmitty

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Posted 14 September 2003 - 12:19 PM

Uh... a giant square drive screwdriver? Actually I should change my diff oil too. I wonder if a 1/2 drive on a ratchet would fit it??? homespun for sure, but make sure you use a Craftsman tool. You break it, they replace it, no questions :D (Probably THE WORST advice I've given so far...)

Bottom line, I don't rightly know. :dead:

ScoobySchmitty :banana:

#3 brus brother

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Posted 14 September 2003 - 12:27 PM

Properly educated with your helpful tips in hand, I will now go watch TV.

#4 Setright

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Posted 14 September 2003 - 12:54 PM

Well, I just had mine changed and only paid for the oil. My local Sube dealer did it, for free, I guess they like me :D

I figure it ain't worth buying the tool since I only change diff oil at the factory 60K miles. Next time is a long time away, and the tool might not fit the next car...

Hmm, that doesn't really help, does it?


SORRY :drunk:

#5 Hawk63

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Posted 14 September 2003 - 01:49 PM

I just did this change on my Legacy. Buy a quart of 80W90 gear oil (synthetic is better) and a gear oil pump (which attaches to the top of the oil bottle, $6). Drive for 15 minutes or more to get the contaminants off the bottom of the differential housing and mixed up in the old oil.

Now use the 1/2 inch drive ratchet directly in the oil plug (lower to drain). This is the same as American cars, but they use the 3/8 drive ratchet. Replace the lower plug and remove the upper plug and pump in the new oil until it runs out. Replace the upper plug and you are done.

Check the Loyale manual for the correct oil weight and capacity.

Also, I'd do this every 50,000 miles to better protect the gears.

#6 ScoobySchmitty

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Posted 14 September 2003 - 02:00 PM

Holy Cheese Batman!

I WAS RIGHT!!!!

(I guess there's a first time for everything...:D )

ScoobySchmitty:banana:

#7 DerFahrer

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Posted 14 September 2003 - 02:17 PM

Originally posted by Hawk63
Now use the 1/2 inch drive ratchet directly in the oil plug (lower to drain). This is the same as American cars, but they use the 3/8 drive ratchet. Replace the lower plug and remove the upper plug and pump in the new oil until it runs out. Replace the upper plug and you are done.



Hold on just a second here!!!

Do NOT remove the lower drain plug first! There is a simple reason: We all know they're not easy to get out. What were to happen if you removed the lower plug, drained all the oil out, then discovered the upper one would not come out with all your might??? You would be royally screwed, since you now cannot refill your diff.

Also, it's better to do that since the air coming in from the upper one will help the oil flow out the bottom one better.

As for oil, it's a differential, so I would recommend Redline 75W90 (not NS) in the rear diff. NOT in a manual tranny though!

#8 theotherskip

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Posted 14 September 2003 - 02:54 PM

a few additional notes...

the service manual recommends putting some permatex ultra-grey around the plug to help it seal when you put it back in.

if you don't have a gear oil pump, you can just use a piece of vinyl tubing. feed the tubing from the rear wheel well down into the diff. have someone pour the oil in while you check that it is flowing ok and not overflowing. it takes a little while, but works.

my plugs were on there somewhat tight, but nothing a breaker bar couldn't handle.

i also changed the manual transmission oil at the same time, but have found that there is a little more grinding when changing gears. i think that the oil doesn't have enough friction for the synchros. i think i'll change it out to redline soon.

i used valvoline 80w-90 for both since it was readily available and not too expensive...

#9 Setright

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Posted 14 September 2003 - 03:50 PM

Hmm, I use Mobil's synthetic in my trans. Saves the pennys at the gas station (European prices!) but shifts need to be deliberate and slow. Wouldn't mind trying Redline, which viscosity and "model" should I go for??

#10 brus brother

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Posted 14 September 2003 - 04:56 PM

The manual calls for 75/90 gear oil for 90 Loyale. There is only synthetic available at my local stores in that weight. I have some 80/90 gear oil and have contemplated using it. Is there that much difference?
I like the through the wheel well, over the shoulder, around the tree approach to the rear diff but I think the $5 pump or even the squeeze bottle the oil comes in with a feeder hose may just do the trick. I will try and post again after I wash the oil out of my eyes.

#11 kevinsUBARU

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Posted 14 September 2003 - 06:58 PM

Ive changed the diff oil twice on my Impreza. I take the top one out first, then the bottom, clean the bottom one up, clean the diff housing, then put the bottom back in. Forget the pump thingie...you can just bend the bottle in half and "baby bottle" it. It works like a charm everytime:headbang:

btw, 75/90 Mobil 1 Synthetic is what I use. If youre going to be towing or anything, get a 80/90 weight

#12 brus brother

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Posted 14 September 2003 - 08:04 PM

Hey Kevinsubaru, I like the simplicity of your method. Did you use the Permatex sealant on the plugs?

#13 sprintman

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Posted 15 September 2003 - 01:12 AM

I concur! Redline 75W90 for the diff (75W90NS for man trans). Up too 6% better fuel economy too and the PE (Group V) base stock handles heat better than anything. My dealer even asked why my trans shifted so good when I had it in for a mid-winter service.

#14 tracedog67

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Posted 15 September 2003 - 07:59 AM

I have heard many good things about Redline oils but where can I get them? I live near Cincinnati so I am near any retail sources?

thanks fellers

#15 DerFahrer

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Posted 15 September 2003 - 10:18 AM

I got my Redline from www.autoil.com, although the last time I was on that site, they only had 75W90NS and no reguler 75W90:confused:

#16 Setright

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Posted 15 September 2003 - 01:59 PM

What's NS?

#17 Strakes

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Posted 15 September 2003 - 02:00 PM

Hey guys, Just curious...
On my limited slip rear diff on a 2002 Legacy GT...would you use Redline 70W90 or 70W90NS? Would you need the NS because it is a viscous limited slip?

#18 brus brother

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Posted 15 September 2003 - 03:29 PM

The question remains, is it necessary to use gray Permatex on the plugs as one suggested.

#19 frag

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Posted 15 September 2003 - 04:08 PM

All I can say is i changed the rear diff oil two times on my Legacy, did'nt put anything but diff oil on the treads and have not had any leaks from there.

#20 DerFahrer

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Posted 15 September 2003 - 05:14 PM

Originally posted by Setright
What's NS?



NS, I believe, does not have friction modifiers, as they don't seem to get along with synchronizers. Therefore, if you were to put synthetic oil in your Subaru MT, which is a bad idea anyway, you would put the 75W90NS in the tranny and 75W90 in the diff...

#21 sprintman

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Posted 15 September 2003 - 06:48 PM

Please present the facts that putting syn oil in a Sube "is a bad idea anyway"

#22 Setright

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Posted 16 September 2003 - 12:42 AM

NS thing is understooded, and I have already started the search for a distributor in Denmark.

I would also like to know why you discourage "syns" :confused:


I am already running Mobil's syn in my MT - and have done so for nearly 60k miles

#23 sprintman

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Posted 16 September 2003 - 12:52 AM

setright you will really appreciate the 75W90NS cold weather shifting performance if you get some. The change over the OEM stuff is very noticeable. Straight 75W90 for the diff. Available from Lubricare International, Taby, Sweden 46-08-756-6596 according to RL's web site.

#24 DerFahrer

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Posted 16 September 2003 - 02:06 PM

I discourage synthetic oil in Subaru MT's because the properties of synthetic oil make it too slick. The synchronizers depend on the friction properties of the oil to get the gears spinning at the right speeds. If said friction properties are not im compliance with the transmission's design, then you will simply grind gears.

I put Valvoline partial syn in my tranny, and ground gears a little. I put straight Redline 75W90NS in, and I'm surprised I didn't completely ruin my tranny, I was grinding so much. I did try adding half GL4/GL5, and that worked good enough, but our trannies are not recommended to carry GL4 oil. So, after a few suggestions, I put regular Castrol dino in and I have not ground a gear since no matter how fast I shift.

I made a BIG brouhaha over on the LegacyCentral BBS about this. Others have followed my advice and report identical results...

Put regular dino in, rest assured you have used the proper oil, and save yourself a couple bucks, since synthetic is not good for our trannies.

#25 theotherskip

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Posted 16 September 2003 - 04:17 PM

i would disagree that synthetic is not good. i put 80w-90 valvoline dino in my tranny and you can feel it hitting gears on almost every shift. it didn't do it with the old oil that was in there (probably original subaru oil). i'm probably going to try the redline as soon as i get some time to switch it out...




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