08 Subaru Legacy GT 5-speed - Trans and Diff Fluid

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JoeFromPA

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Hi all,

Looking for recommendations on the most effective solution to my desire to swap trans/front diff and rear diff fluids in my 2008 Subaru Legacy GT.

The transmission is somewhat clunky to shift stock, and many owners report substantial improvements in shifting from switching to a quality synthetic (such as Subaru Extra-S (new) or Redline).

The car runs 75w90 (without friction additives) in the trans and front diff (no LSD) and 75w90 (with friction additives) in the rear diff (does have an LSD).

I'm trying to find a cost effective and really "best" oil for reducing my shifting notchiness, shifting resistance, slight gear noise, and even occasional lock-out from reverse. Again, owners who have swapped have reported improvements in all those areas so I don't think I'm being unrealistic.

My options so far:

-Redline 75w90 for rear diff and 75w90 NS for Trans/Front Diff. About $10 per quart.

-AMSOIL Severe Gear 75w90 for rear diff and a bottle of friction modifier to ensure no chatter occurs. $13.25 or $11 per quart (might re-up my membership), $7 for LSD additive.

-Subaru Extra-S fluid - Sold in only two shapes....$20 per quart or $135 for a 5-gallon container. LSD additive is around $5-10 I believe.

-Valvoline 75w90 synthetic - Not sure how much this costs, but it was recommended as a lower cost option. Need an LSD additive I believe.

Any thoughts, recommendations, pointers, links, or tips are very appreciated.

Thanks for your time!

Joe
 
I vote for the Severe Gear, maybe even in the 75w-110 if you do any rallycross/autocross. My Subie loved the stuff.

Unless the diff is a clutch-type that is very tight, you should not have to add any friction modifier to the rear diff...viscous diffs are sealed and do not require FM, and clutch-types that have too much FM added (even 0.5oz) can slip like crazy....the point is to have it lock up firmly and evenly. I'd just add the gear oil, drive it for a day, and if it is chattering under VERY HARD and tight cornering, then add 0.5oz increments.

Choice #2 would be the Subaru Extra-S. I had used that and Motul Gear300, but settled on the AMSOIL as my favorite for shifting and less gear whine.
 
I agree, the Amsoil is an excellent product. Send a PM to either Pablo or Gary Allen and they can help you with this product. I believe Gary Allen is also in PA.
 
Hey gents,

Thanks for the great feedback. Every Subie owner I know has either:

A. Run Redline 75w90 with friction modifiers (i.e. not the non-slip version).

B. Added friction modifier to the rear diff.

Will AMSOIL 75w90 Severe duty be sufficient for both front and rear with no additives?

This is my wife's daily driver, so we probably won't be doing any seriously hard driving, rallying, road races, or AutoX....we just want a really good oil with smooth shifting and a quiet drivetrain.

Joe
 
If you get the Amsoil, I'd suggest the 75-110.

Both titan and I put in 75-90 SVG and our diffs had some noise.

Adding some 140 took care of my whine.

Get with Pablo on the straight scoop.

Bill
 
Originally Posted By: Pablo
You'll need to run Amsoil 75W-110. (Redline is behind the times on recognizing the new SAE gear oil viscosities)


beat me by 34 secs!
grin2.gif
 
A 110 weight in a trans rated for 75 weight?

That seems like it's tempting fate....was there an SAE gear oil grade change where 90 weight is now 110?

Joe
 
Originally Posted By: JoeFromPA
A 110 weight in a trans rated for 75 weight?

That seems like it's tempting fate....was there an SAE gear oil grade change where 90 weight is now 110?

Joe


It's 75W-90, not "75 weight". W indicates the cold temp flow characteristics, specifically a MAX temp for viscosity of 150,000 cp. For 75W it's -40°C. And yes there was a change:

http://www.lubrizol.com/products/automotive-gear-oil/J306.asp
 
Sorry, I typed that in really poorly and I use "weight" to refer to viscosity (rightly or wrongly).

I read the change and can see why 75w110 can be used in place of 75w90....it seems like the 110 rating has the same maximum kinetic viscosity at 100 degrees celcius, but has a higher minimum kinetic viscosity at that temperature. Did I read that correctly?

Sounds like 75w110 is the one for me....not cheap, but as long as it smooths out the shifting and quiets the gearbox, I'll be happy as a pig in....well, I'll be happy.

Joe
 
Another happy Severe Gear owner here, although I went with 90 in the front and 110 in the rear.

BTW, I don't think the Extra-S is synthetic.

MSDS

Now the link isn't working but it states:
"PREPARATION DESCRIPTION:
BLEND OF HIGHLY-REFINED MINERAL OILS AND ADDITIVES"

-Dennis
19.gif
 
Originally Posted By: JoeFromPA
..............Every Subie owner I know has............B. Added friction modifier to the rear diff..................


Why??? The Legacy does not use a clutch type limited slip, and therefore does not require a friction modifier. It won't hurt anything, but it is not required. The GT uses a viscous coupling in the rear, and the SpecB uses a Torsen in the rear. Neither require a friction modifier.
 
Last edited:
I run the Extra S in my 2008 Legacy GT and that's what I would recommend. Mine shifts like a real car with this oil. It has exactly the right friction characteristics for Subaru transmissions.

My WRX transmission was a total POS, and was very fussy about oil. The Legacy GT transmissions are much, much better.
It sounds like others are having good luck with other oils in the Legacy transmission, so any of the the oils in this thread would be a good choice.

There is no need for a friction modifier in the rear differential. The limited slip is a sealed unit that contains a silicon fluid.

Ed
 
Then why the heck does Subaru sell an LSD oil specifically for this purpose on their LSD-equipped models?

I won't add the LSD oil (that's what Subaru calls it), but it does imply the need for friction modifiers in these diffs...

Joe
 
Ed -

You are not the first or last person to be very complimentary to Exra-S. I'd go for it except:

$20 a quart is very expensive and only available from Turn-in Concepts, a company which takes it out of 5 gallon containers, quarts it up, and ships it out (although it IS $20 a quart shipped...)

5-gallon containers are too much to keep around for just one Subaru

Dealerships charge a good amount for this stuff swapped in (though I am awaiting a quote right now).

Joe
 
Originally Posted By: JoeFromPA
Then why the heck does Subaru sell an LSD oil specifically for this purpose on their LSD-equipped models?
Joe

They do? Do you have more details? You're not thinking of the STi rear diff gear oil, are you?

-Dennis
 
The 90LS oil you linked to is for Subarus with a clutch type LSD in the rear, such as '06 STI.

From an IWSTI thread on this topic:

"Hello Richard:

Thank you for your patience. I researched this in our Technical Service Manuals. No, the LSD gear oil used in your 2006 WRX STI is not used in the 2007 WRX STI. In the Technical Service Manual for your 2006 WRX STI Sedan, it states:

Mechanical LSD oil MUST be used for STI model. Recommended oil - Gear oil LSD (Subaru part # K0305Y0900), GL-5 (90) or equivalent.

In the Technical Service Manual for the 2007 WRX STI Sedan, it states:

Recommended gear oil: GL-5 (75W-90) or equivalent.


For the 2007 WRX STI, the Subaru Extra Gear Oil (75W-90) was used at the factory for the rear differential and manual transmission.

Sincerely,

John
Subaru of America"
 
Awesomeness....so now it's just a matter of picking up 5 quarts of AMSOIL 75w110.

Random question....if I'm a member, can I get the member prices from a local distributor or only from ordering online?

Joe
 
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