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Discussion Starter #1
Can someone please explain to me how these two systems differ, either in theory or in execution? The Subaru AWD on demand that comes with the 4EAT sounds as if it splits torque between front and rear starting from a stop, then slowly transfers torque until most of it is with the front wheels once the car gets to cruising speed. It then monitors the wheels and sends torque to those with traction if it detects that some wheels have less traction. Does this sound about right? The description of the iTM3e (from wikipedia) is as follows: "Multi-plate clutch coupling. The ITM 3e multi-plate clutch coupling is used in the Hyundai Santa Fe , Hyundai Tucson and Porsche 911. In normal conditions it send up to 95% of the torque to the front wheels. In the case of the Hyundais, the system can be locked in a 50:50 split so that you have a more dedicated off-road system. The system can be locked with the '4WD LOCK' button. The ITM 3e uses a multi-plate clutch coupling with magnetic activation" If anything this sounds better since with the push of a button you can lock in a 50:50 split. Can anyone tell me how subaru's system is different, or if it functions basically the same way and results in the same performance? Thanks in advance.
 

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Similar to the borgwarner. In 1&2 it basically locks it, and theres a mod to wire in a switch to force the MPT (multiplate transfer clutch) to lock. It monitors the front and rear and adjusts, but it can't target the individual wheels (although with VDC it can use the abs to brake individual wheels).

In some foresters, and in the 5speed autos, theres a VTD center diff, a planetary diff instead of the MPT, which is a much better setup (and I wish I had it!)
 

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Discussion Starter #4
This is all very interesting, thank you. So if I am understanding correctly a 2010 Forester has an MPT electronic clutch system, and not a VTD center diff. And this would likely be similar in operation / function to a 2010 Hyundai Tucson with the Borg Warner system, and possibly even to the system on the Mitsubishi Outlander? I have to imagine that the overall design of the forester, with a lower center of gravity and better clearance would still outperform it, but it seems that their AWD systems are quite close. Additionally I am curious as to how well the VDC can mimic the functionality of a LSD. My understanding is that if you have three wheels with no traction, say the rear two and the front right wheel, the AWD system will split the torque (relatively) in half as it detects slipping on each axel, and then the VDC can come in and brake the spinning front right tire, which redirects some of the torque to the front left tire, which allows one to gain traction and get out of the snow / sand / mud that they are stuck in.
 

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Smooshed FOTY 2011
2005 Lifted 2.5 XT 5-Speed MT Dual-Range
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VDC really doesn't mimic an LSD, it works much MUCH better. The LSD is pretty much worthless off-road. In just about all situations where the LSD should help out, it doesn't do enough (if anything at all). The VDC system applies brakes to the wheel(s) that are spinning, which gives power to the wheels with traction. This pretty much eliminates the "diagonal spin" and is extremely beneficial off-road, and works very well.
 

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There are some really good examples of how the subie system compares to other "awd" models. In my experience it is as good as a true 4wd system that locks front and rear together. It can definitely get out of some sticky or sandy situations with ease.
 

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2008 Forester X Premium 5MT
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VDC really doesn't mimic an LSD, it works much MUCH better. The LSD is pretty much worthless off-road. In just about all situations where the LSD should help out, it doesn't do enough (if anything at all). The VDC system applies brakes to the wheel(s) that are spinning, which gives power to the wheels with traction. This pretty much eliminates the "diagonal spin" and is extremely beneficial off-road, and works very well.

True, VDC best mimics the function of a locker.
 
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