Subaru differential fluid change....

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OK, so my moms car is a 2002 LL Bean Outback, which has the H6, 4 speed auto and a limited slip rear differential. I know there are front and rear differentials, but I always see references to the "center differential". Is this a third differential that I am going to have to change the fluid in, or does it share fluid with the transmission, or am I misunderstanding something completely?

There are currently 4 fluids I am considering for the job. Amsoil Severe Gear 75W-90, Amsoil Long Life 75W-90, Redline light weight Shockproof, and Redline 75W-90.

Does anyone have any input on my fluid choices?
 
Since it is an auto, there are three drive train fluid sumps.

- Transmission, which is an ATF of some sort (the fill/dipstick is located on the DRIVER'S side, near the firewall)

- Center Differential, which is a combination differential and transfercase (the fill/dipstick is located on the PASSENGER'S side, near the firewall) - 75w90 Gear Oil

- Rear Differential - 75w90 Gear Oil

Make sure you remove the fill plug on the rear diff before removing the drain plug...you don't want to drain your fluid to find you can't remove the fill plug!!
 
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Originally Posted By: chevrofreak
So the center differential and the front differential are the same thing?


they are 2 different components sharing a common housing and sump.
 
Originally Posted By: Pablo
Also consider Amsoil 75W-110. Most car mfr's are still using old specification language.


Part of why I was looking to go with the thinner stuff like the Redline light weight shockproof is that her car has been getting poor fuel economy lately* and that I want to do everything possible to increase it. She's getting a max of 22.25mpg in a car that should do 26. I'm using synthetic engine oil, it has a new air filter, and I've used Amsoil P.I. in the fuel recently. Still not enough of an improvement.

* might be that this valve is rusted shut. The bypass pipe has some rust holes in it, and the nuts on the cover are so rusted I can't get them off, so that's what makes me suspect a rusted shut valve. I'm probably going to replace the muffler with a glasspack or piece of straight pipe
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Originally Posted By: bdcardinal
Originally Posted By: chevrofreak
So the center differential and the front differential are the same thing?


they are 2 different components sharing a common housing and sump.


Thank you, that clears a lot up. I was worried that there was another separate differential that I was not aware of.

Fortunately, it looks to be extremely easy to change out the fluid in the front and rear differentials.
 
Originally Posted By: chevrofreak
Fortunately, it looks to be extremely easy to change out the fluid in the front and rear differentials.


funny story about that, one of the shops i worked in, the customer got a free front/center diff and trans fluid change with an oil change thanks to a manager to refused to listen to me when i pointed out that there was more than one dipstick.
 
Stay away from the Shockproof. Many of us Subaru guys have had problems with it turning to jelly in the bottom of the trans/center diff.

I've had great luck with Amsoil SVG 75w90 for the front & rear diff.
If your rear diff is making any noise, (many 02-04's do) then run SVG 75w110 and it'll quiet down.

Redline 75w90 is also a great choice.
 
I did read about some issues with the Subaru's and the Heavy Shockproof, but the Light Shockproof is no good either?

I do think I'm probably going to end up going with the Amsoil 75W-90 Severe Gear on her Subaru, and putting it in my 96 Crown Vic while I'm at it.

The Redline 75W-90 is still an option, because it's the cheapest of them all. I can get 5 quarts for $53 shipped. I may have to flip a coin...
 
I emailed Redline regarding the 75w90 and the 75w90NS. They recommended the 75w90,not the 75w90NS. Just thought I'd mention this in case you go with Redline.
 
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The Redline 75W-90 is a very good possibility at the moment. I need 5 quarts to do both my car and my mothers car, and I can get it on Ebay for $52.95 shipped. From the local Amsoil dealer the 75W-90 Severe Gear would be $66.25

Each of these oils has their strong points, with some performing better in certain tests.
 
unless subaru changed things, the AT does NOT have a center diff. It has an electronically modulated limited slip clutch. It is a fwd car with rwd assist. Silicone-based, non serviceable unit IIRC.

The manuals have a center diff with limited slip clutchpack. these are more of a awd/4wd architecture.

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Originally Posted By: meep
unless subaru changed things, the AT does NOT have a center diff. It has an electronically modulated limited slip clutch. It is a fwd car with rwd assist. Silicone-based, non serviceable unit IIRC.

The manuals have a center diff with limited slip clutchpack. these are more of a awd/4wd architecture.



The last sentence is more or less correct - manuals have a centre diff with viscous limited slip. The WRX uses the DCCD system, where the driver can control the front/rear torque split or let the computer do it all.

There are currently four types of AWD used by Subaru. Read about them all here - http://home.comcast.net/~a6n6d6y/andy/Subaru AWD.pdf

Since the OP's vehicle in question is an automatic, I've pasted the two pertinent sections below. The 2nd section (VTD) mentions VDC. This is Vehicle Dynamic Control, which is not an AWD system, but a stability control system like Honda VSA, GM stabilitrak, Mercedes ESP etc.


________________________

2. Active Torque Split - Multi-Plate Transfer Clutch System

This computer controlled electronic constant All-Wheel Drive system is specifically designed for automatic transmission vehicles. Basically, it automatically transfers power from the wheels that slip to the wheels that grip for improved traction.
Subaru’s expertise in electronically controlled All-Wheel Drive dates back to 1981. Since then, the company has accumulated a wealth of technological expertise and capability in producing an industry leading automatic All-Wheel Drive system. The Active Torque Split system uses a computer to electronically control the hydraulic fluid pressure in the Multi-Plate Transfer (MPT)clutch, at the rear of the transmission that directs the drive to the rear axle. This computer works together with the automatic transmission to measure and monitor information including speed, gear range, accelerator position and rotational speed differences between front and rear wheels. This input information is then used to calculate and apply optimum torque to the wheels, according to driving conditions. For example, if the front wheels are on a wet or slippery surface and the rear is on dry, more power will be transferred to the back wheels.A key advantage of this system is that it can continuously vary the drive power to the front and rear as required to prevent slippage. At the same time, it also controls the All-Wheel Drive system to maximise the effectiveness of the Anti-lock Brake System (ABS). In situations that require more traction, the system can vary drive split up to 50:50 for maximum traction and grip. This sophisticated coordination of systems ensures greater safety on slippery roads and during acceleration, or braking to avoid accidents.

______________________________


3. Variable Torque Distribution (VTD)

Variable Torque Distribution is a revolutionary and highly sophisticated system for automatic transmission vehicles. This system maintains the high stability of All-Wheel Drive with
a more sporty cornering performance and feeling normally associated with rear-wheel drive vehicles – ideal for high performance cars such as the automatic Liberty 3.0R spec.B.
The LSD in this system is controlled electronically, via a multi-plate clutch. This means that it can adapt to the driving conditions such as slippery surfaces and under hard cornering,
by varying the torque distribution between front and rear wheels.
Under normal circumstances, the VTD torque distribution has an emphasis on the rear wheels. This reduces understeer normally caused by hard cornering acceleration, resulting in smooth and sporty handling. In situations that require more traction and grip, VTD can automatically change the torque distribution to a maximum of 50:50 front:rear. When used in conjunction with Subaru’s advanced Vehicle Dynamics Control (VDC), it optimises vehicle control by seamlessly correcting oversteer, reducing understeer and maximising traction and grip. In essence, it complements the vehicle’s AWD capabilities by using it as the first line of defence against losing control.
 
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Fogot to mention to the original poster, you probably have the active torque split system in the LL Bean (unless you have VDC emblems on your car).

The H6 VDC limited had the VTD and VDC.
 
I have used Schaeffer's #293 in both differentials of my 2004 Outback and I really like the way it seems to handle. The front differential drain-plug on mine is a T-70 Torx; perhaps to keep quick-lube places from accidentally draining it!? Lisle tool make a T-70 for this purpose....
 
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