Auto Technology

Subaru celebrates 15 million AWD vehicles

Boxer engine and equal-length half shafts create symmetrical system

Subaru Symmetrical AWD

There are two famous all-wheel drive systems in the world. One is Quattro fitted to the Audi upscale brand. The other is Subaru’s Symmetrical Full-Time All-Wheel Drive, which recently celebrated the 15-millionth vehicle so equipped to come off the line.

The system is made up of a horizontally opposed (Boxer) engine and transmission balanced over the front axle, which is made up of equal length half shafts (as is the rear axle) — giving it the “symmetrical” moniker — helping to lower the centre of gravity of the vehicle in which it’s equipped.

The father of the modern system was created for the 1972 Leone Estate Van, and has undergone several changes and tweaks in the 44 years since. Today, it is made up of four variations (depending on transmissions and applications) and is marketed on 98% of Subaru models sold worldwide, and all vehicles sold in Canada, with the exception of the BRZ sport coupe co-developed with Toyota.

The first Subaru equipped with the Symmetrical Full-Time All-Wheel Drive system was the 1986 XT coupe, in the non-turbo, automatic transmission model, with an electronic torque split version coming along a year later. That pegged the default distribution at 60% front and 40% rear, with the ability to change the distribution to a max of 50:50.

Active torque split all-wheel drive is today found on automatic versions of Subarus, whether they are continuously variable or those with traditional gears.

Variable torque distribution came along in 1991, in the classic SVX coupe, with the default being 36% front and 64% rear (changing to 45:55 in later versions). Today, it is exclusive to the WRX equipped with the Lineartronic CVT.

Today’s manual transmission Subarus use Viscous Coupling Centre Differential AWD, with the exception of the WRX STI. The viscous-coupling limited slip centre differential maintains a 50:50 front/rear torque split.

The WRX STI uses Driver Controlled Centre Differential AWD that allows the driver to adjust the centre differential from 41:59 front to rear distribution to 50:50. This industry-unique system also uses a helical-type front differential and a TORSEN (torque sensing) rear differential, creating a triple-differential set-up.

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