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What is a vehicle’s differential? There’s a gearbox between the drive wheels of your new Subaru. If it’s an all-wheel-drive system, then you’ll nearly always have a front and rear differential. This gearbox works with your vehicle’s transmission to send power from the engine to the wheel’s axle, which stabilizes your vehicle’s turning. When you turn, for the best grip, you need the outside wheels to turn faster than the inside wheels, and a differential uses gears to accomplish this. This is why it’s crucial to keep up with your vehicle’s maintenance at our Service Center, including changing out your differential fluid every 30,000 to 60,000 miles.

Subaru vehicles have different differentials for various models, all designed to improve grip, turning capability, and overall safety. These systems include Viscous Center Differential (VCD), Active Torque Split (ATS), Variable Torque Distribution (VTD), and Driver Controlled Center Differential (DCCD).

Viscous Center Differential (VCD) will provide a 50/50 torque split between the front and rear tires. The brakes are used to reduce slip and improve wheel torque, by sending breaking signals to a spinning tire. If an axle starts to spin, the viscous coupling forces torque to the wheel with more traction, whether that’s the front or back. This VCD system is is included in manual transmission models, like the Crosstrek, Impreza, and Forester.

Active Torque Split (ATS) has a 60/40 torque split for the front and rear. This system is actually different, because it includes a multi-plate center clutch pack, rather than differential, which allows for slip and is always partially engaged. Being “active” means it’s continually looking for more than just wheel slip, but also takes information from all available sensors and determines whether there may be a loss of traction and provide adjustments. You’ll find this on models like the Legacy and Outback.

As for the Variable Torque Distribution (VTD), which is only available in select Subaru vehicles like the WRX, is made for vehicles that need to accelerate quickly. There is a 45/55 split between the front and rear wheels, giving you more back-end grip and an electronic hydraulic transfer clutch, sending lock-up to the wheels that need it.

Finally, the Driver Controlled Center Differential (DCCD), exclusively in the STI, is an incredibly sophisticated system, which not only includes a limited slip differential, but also an electronic differential. There is a 41/59 split between the front and rear. The multi-plate clutch and transmission control module made adjustments based on sensor input, but the driver is also able to have control over what’s happening. No matter what scenario you’re facing, you’ve got everything you need to get the right traction to whichever wheels need it.

Categories: Service, Parts