Viscous Center Differential (VCD)
Subaru's Viscous Center Differential is the tried and true differential. The VCD differential has been used on all manual transmission models, and is entirely mechanical. VCD differentials from Subaru split the power 50/50 between the front and rear wheels. VCD differentials engage when one wheel loses traction, which causes the viscous coupling to send power to the wheel with more traction.
Active Torque Split (ATS)
Some of Subaru's most popular models use a different type of differential, called Active Torque split. Subaru's Active Torque split (ATS) is used on all continuous variable transmission models. ATS differentials from Subaru split the power 60/40 between the front and rear wheels. The Active Torque Split system uses a combination of a clutch and open differentials on the front and rear axles. The ATS system is considered Active, as it is controlled and engaged electronically by sensors, rather than after slippage and loss of traction has already started occurring.
Variable Torque Distribution (VTD)
Another type of differential used by Subaru in select models like the CVT WRX, Variable Torque Distribution from Subaru favors power to the rear axle with a 45/55 split of power between the front and rear. The purposes of the VTD system are to improve handling under intense cornering conditions to avoid or reduce understeer.
Driver Controlled Center Differential (DCCD)
The final type of differential currently available from Subaru is the Driver-Controlled Center Differential. This option also favors power to the rear axel with a 41/59 split, and is much more advanced than other systems, combining mechanical, and electronically controlled, driver engaged differentials to fine tune the handling of a vehicle in performance driving.
What is it?
A differential is basically a set of gears that lets the wheels of a vehicle on a single axle to spin at different speeds. This is important, because when going around a corner, one wheel needs to turn faster or slower than the other.
A rear differential connects the power source of the vehicle to the wheels. The set of gears inside of the differential allows for the power transfered to the wheels to be adjusted based on which wheel requires the power.
The differential is a key component for all vehicles, but is particularly important for all-wheel-drive vehicles that rely on power being delivered to the wheel and tires that needs it most.
There are different types of differentials that function differently to achieve the same goal. Subaru uses different types of differentials in their models, including viscous coupling differentials that are entirely mechanical, and electronically controlled Variable Torque Distribution (VTD) that use sensors to detect slipping wheel that are quicker and more responsive than mechanical alternatives.
What does it do?
A differential accounts for loss of traction on individual wheels, and changes the amount of power going to that wheel to adjust. For example, consider a a rear wheel drive car that has one wheel in a pile of snow, and another wheel on drive pavement. When the tire that is in the snow starts spinning due to a lack of traction, the differential will engage to send the engine's power to the wheel that is on dry pavement.
In everyday driving, the differential is also used when going around corners, to allow for the wheels to turn at different speeds to go around the corner.
When to Replace?
With regular maintenance, and regular driving conditions, a differential should last quite a while. Since a differential is a bunch of moving gears, it requires lubrication, and regular service.
Particularly on all-wheel drive vehicles, the differential should be inspected, and have fluids changed regularly. Consult with your Service Advisor at Whitby Subaru to determine the recommended schedule for your particular Subaru model.