[Brettnrs423]

Hi guys. Im currently at the 30K mark and want to change out my differential fluid. I already completed the tranny fluid, but am unsure of what fluid to use for the rear end. I have a quart of mobil 1 synthetic 75W-90. Will this be sufficient, or do I need an lsd specific oil. Also...i know that you need to put liquid gasket on the plugs when reinstalling them. Will pretty much any silicone based liquid gasket that has a resistance to oil work? I have seen the manual and know that Subaru recomends there oil, but will the Mobil work, and if not can i buy an lsd additive for it? If not mobil...what other brands of oil that I can find at stores should I look into? Thanks in advance.

[solbergfan]

The rear diff is a clutch type LSD so you should use a specific type of gear oil. Other than the Subaru stuff (which no dealers stock) the only thing I've seen is Motul 90PA LSD oil. I just changed the rear diff fluid on mine a few weeks ago and used it. I got it here:

http://www.performanceoilstore.com/p...sp?prod=318121

It comes in a 2 quart bottle-the diff holds about a quart.

[Brettnrs423]

Thanks solbergfan. Can anyone else confirm that this is the only oil that can be used in the differential other than the stock fluid? Also does anyone know what kind of liquid gasket I need?

[QuickSilverSTi]

A few threads down...:

What you need for a rear differential fluid change

[Brettnrs423]

Thanks nhluhr. I actually managed to get the oil from Subaru and do it right. The pump to put the oil in was a major POS, oil spilled everywhere, and it took for ever to pump the fluid in. Other than that it was pretty straight forward.

[sciolist]

Maybe this is a stupid question, but why is the 90LS identified as being specific to the rear differential? What are people using in the front?

Also, what is the capacity of the front differential?

[Singletrack]

Originally Posted by sciolist

Maybe this is a stupid question, but why is the 90LS identified as being specific to the rear differential? What are people using in the front?

Also, what is the capacity of the front differential?

Front diff is integrated with the tranny, so they share the oil. I just switched over to Valvoline 75w90 at 30k. Seems a touch notchier than stock, but pretty comparable. It's hard to judge also since the weather just changed and it is cooler now.

[sciolist]

Okay, so I guess that was a relatively stupid question.

Seems like the tranny would be the governing parameter in terms of oil. I certainly want to optimize the smoothness of the shift actuations, but there doesn't seem to be much evidence that anything works better than the OEM oil for any significant period of time. I'm reluctant to even waste my effort with synthetic. What do you think?

[Singletrack]

Originally Posted by sciolist

Okay, so I guess that was a relatively stupid question.

Seems like the tranny would be the governing parameter in terms of oil. I certainly want to optimize the smoothness of the shift actuations, but there doesn't seem to be much evidence that anything works better than the OEM oil for any significant period of time. I'm reluctant to even waste my effort with synthetic. What do you think?

No one really knows what the stock fluid is unfortunately : ( It really isn't clear if it is dyno or synthetic either, just that it is 75w90. There is an ambiguous oil analysis on this site if you do a search. I used Valvoline 75w90 because people have had good results with it.

[Rev]

Good call on the 90PA LSD oil ... I wouldn't recommend Gear 300 on the rear diff either, it's prone to causing chatter during turns, nor Mobil1 75W-90. I think the only way to go is dino...

[Rev]

Originally Posted by nhluhr

I don't see anything wrong with synthetic as long as it is a specifically engineered LSD oil. In this case, the Subaru Genuine stuff or the Motul LSD oil which is a synthetic.

The Motul oil says "mineral" at the bottom

[sciolist]

So then 90LS in back and Gear 300 75w90 in front? Is anyone having synchro problems with the Gear 300?

[kwantam]

I've heard several reports of excellent performance in the STi with products from Specialty Formulations. For the tranny/front diff, I'm planning on switching to MTL-R, and for the rear diff I'll use HDS-5.

I've posed a quick question to the proprietor of SF to make sure these are the lubes he'd recommend; if I hear any differently, I'll post it here.

-kwantam

[Riceman]

Anyone ever try Red Line Oils kit, below is the description off of their site:

Subaru WRX PowerPack
Reduced turbo lag, smoother shifting, improved fuel economy and cooler operating temperatures are among the benefits of the WRX PowerPack from Red Line Oil. Dyno testing shows significant horsepower and torque gains all over the power range.

Included in the kit are 5 quarts of 5W30 motor oil, 4 quarts of 75W90 NS gear oil for the transaxle, 1 quart of 75W90 gear oil for the rear differential, 1 bottle of WaterWetter for the radiator, 1 bottle of SI-1 Complete Fuel System Cleaner, a sticker kit and a Red Line Oil embroidered hat.

Note: Due to the WRX STi 6-speed transmission's capacity, an extra quart of 75W90 NS is required and is reflected in the price of that particular kit.

$119.00 for the STi, could really do without the stickers and a hat, just wanted to get some input on it.

[solbergfan]

Originally Posted by Riceman

Anyone ever try Red Line Oils kit, below is the description off of their site:

Subaru WRX PowerPack
Reduced turbo lag, smoother shifting, improved fuel economy and cooler operating temperatures are among the benefits of the WRX PowerPack from Red Line Oil. Dyno testing shows significant horsepower and torque gains all over the power range.

Included in the kit are 5 quarts of 5W30 motor oil, 4 quarts of 75W90 NS gear oil for the transaxle, 1 quart of 75W90 gear oil for the rear differential, 1 bottle of WaterWetter for the radiator, 1 bottle of SI-1 Complete Fuel System Cleaner, a sticker kit and a Red Line Oil embroidered hat.

Note: Due to the WRX STi 6-speed transmission's capacity, an extra quart of 75W90 NS is required and is reflected in the price of that particular kit.

$119.00 for the STi, could really do without the stickers and a hat, just wanted to get some input on it.

That's fine for the WRX but the STi needs a specific rear diff oil (read the above posts) and the 6 speed does not seem to like synthetic gear oil-most people seem to have problems with it, but some don't. The ones that don't have problems use Motul Gear 300. Stick with dino for the trans and LSD oil for the rear.