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.
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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.
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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.