There are threads on this going back to before the Flood, if you care to run a search.
In the US transmission the rear drive is operated by an electro mechanical clutch. Your power distribution is normally about 85/15 % with front bias, and the TCU uses the solenoid duty cycle to give more power to the rear as required up to a maximum of 50/50.
This gearbox is described by Subaru as "Active Torque Split AWD system".
The gearbox fitted to Japanese and UK cars, and certain other markets, is different. It is a full-time 4WD gearbox with similar power distribution to the manual system as used in the WRX. It uses a centre differential [as opposed to a rear take-off] which normally sends 64% of the power to the back and 36% [approx] to the front.
As the rears start to slip under power, the TCU can randomly divert power to whichever wheels have grip up to 50/50.
This type is described by Subaru as "VTD-AWD system"
This difference is notable also by the use made of the AWD fuse under the hood. In the US car, like yours, Snow, if you insert the AWD fuse it turns the AWD system OFF. You end up with a car driving 100% of the power to the front wheels, it disengages the rear take-off clutch.
In the UK cars if you insert this same fuse it
locks the centre differential at 50/50. Effectively this means we could not drive our cars too far with the fuse in, at least unless we were on the loose. You guys could actually drive yours with no real problems, this is a bonus your SVXs have that ours don't enjoy.
With the US type AWD fuse turn-off system it is possible to test your cars at a test centre having only one roller for the dyno, by fitting the fuse temporarily. It is postulated that this is the reason these gearboxes were supplied in the USA, but nobody has ever confirmed that.
With my car it is permanent AWD and the local test centres are unable to test it on the rollers [they don't have double rollers] for brake function and so on. In order to complete the tests, the guys have to bring the SVX for a short drive. They seem quite happy to do this.
Joe
