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Discussion Starter #1
Before I get flamed, I'll admit that I obviously don't know a lot about our cars/or cars in general. But I am in a huge debate with some chumps at my work that probably don't know much more than me but insist that our cars aren't all wheel drive all the time.

I went to subaru's website and tried to find out that way, but the information seemed to contradict itself and is also confusing. It claims symmetrical which would lead me to believe that all the wheels produce power at the same time, and it says continuous all wheel drive, which would mean all the time. I know that 4 wheel drive systems work so that only one front wheel actually produces power, and one rear wheel produces power...unless equipped with a limited slip diff., or locking mechanism, then the other wheel would engage under slippage or w/a locker it would always produce power.

I guess my question is: how do our systems work, since we do have limited slip diffs. is it the same or is our system completely different? Sorry for sounding ignorant as all hell....but I am. Any info would be appreciated.
 

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Subaru All Wheel Drive (AWD). There are 3 systems- Continuous, Active and VTD

Continuous AWD: Subaru manual transmissions use Continuous AWD, normally 50/50 front-to-back power split and use a mechanical viscous center differential to to vary the power split when there is a loss of traction.

Active AWD: Subaru's automatic transmission use Active AWD, mostly front wheel drive and uses traction sensing computer input to electronically vary the front to rear power split via a hydraulic multi-plate transfer clutch. This is on all non-WRX automatic models It is a 90 F/ 10 R split.

VTD AWD (variable torque distribution). New in 2001, VTD transfers powers front to back electronically. The power split is 45/55 front/rear and the rear wheel bias is designed for a more luxury car feel as opposed to the front bias of the Active AWD system. Usually 45/55 front to back split but that varies according to wheel slippage. This is for the automatic wrx's They also have VDC, which is explained below.

Limited Slip Rear Axle (rear differential): Limited Slip transfers power to rear wheel with best traction. Also known as Posi-traction. Available on all WRXs and some other models.

VDC is used on certain models (such as auto wrx's)and is also the name of an Outback Limited model. New in 2001, this is VDT all wheel drive combined with VDC full time traction control and engine management.

Composed of VTD (variable torque distribution) All Wheel Drive system and VDC (vehicle dynamic control)
VDC: (vehicle dynamics control)
The overall name of the system, and also of the Outback VDC model.
VDC is traction control that senses vehicle direction and then uses brake, throttle and engine management to control and maintain stabilty.

The components of the VDC system are:
all wheel drive using the VTD system (see above).

When the wheels are spinning without traction or the vehicle is not going in the direction it is being steered, the VDC (variable dynamic control) engine management system kicks in.....
it uses the brake system to slow down one or more wheels to reduce and stop spin and thus control vehicle direction.

It also uses engine output to slow spinning by reducing spark to cylinders to cut back power and help re-gain control


Hope this helps
 

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Discussion Starter #3
Thank you brandonwrx, that does help. But, I guess my main question is: are all 4 of the wheels producing power, or is it one front and one rear, then the other wheels are passive then engage only under slippage. Sorry if I sound redundant and you may have already addressed this question, and I just couldn't decipher the language.
 

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Auto wrx's use active AWD with VDC and VTD...active being the key word here. All 4 wheels continuously have power, and in normal situations the power is split 45/55 front 2 wheels to rear 2 wheels. The rear limited slip transfers power to the tire with the most grip (spinning slower on a slippery surface).
With the VTD, the split between the front 2 and rear 2 wheels could be as high as 10/90 or 90/10 depending on conditions as well as a split 0/100 and 100/0 between the rear 2 wheels.
 

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It's all good. If you have a 5-speed you have "Continuous" AWD. A center Viscous Limited Slip diff transfer power front/rear 50/50 in normap operation. When it senses slip it transmit power to the wheels (front or rear) with MORE grip. The front Diff is open on WRX so whichever wheel has LEAST traction will spin. THe rear has Viscous Limited Slip diff. Same as the center only this distributes power between the 2 rear wheels instead of front/rear.

Does that help?
 

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This needs to be stickied.

A friend got in my car and expected it to have some sort of DCCD-ish controller just because it was AWD. I said that I didnt but didnt know exactly how the system worked.
 

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tarbaj said:
It's all good. If you have a 5-speed you have "Continuous" AWD. A center Viscous Limited Slip diff transfer power front/rear 50/50 in normap operation. When it senses slip it transmit power to the wheels (front or rear) with MORE grip. The front Diff is open on WRX so whichever wheel has LEAST traction will spin. THe rear has Viscous Limited Slip diff. Same as the center only this distributes power between the 2 rear wheels instead of front/rear.

Does that help?
Some people have said that the rwd bias of the automatic helps them get into powerslides. The wagon has a closer 50/50 weight distribution, and 50/50 power distribution, and I find that I can whip it around fairly well as such.

-snowcat
 
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