The car's differential is responsible for getting the energy, or torque, from your engine's drivetrain to the wheels. In a two-wheel drive vehicle, there would only be one differential which would be either in the front or the rear of the car depending on its drive layout. For all-wheel drive and four-wheel drive vehicles, there would be two differentials, one in front and another at the rear.

The torque is transmitted from the engine and transmission through a driveshaft to power the differential, which contains a side gear, ring gear and pinion gear. The differential then turns the torque through its series of gears, sending the rotating motion to the wheels. 

There are several types of differentials, and we will take them up in this article.

Open Differential

The open differential has been around for a long time and is the most common type. When a car turns around a bend, the open differential goes to work. It allows the inside wheel to rotate slower than the outside wheel. This type is commonly found in family sedans, crossovers, minivans and economy cars.

The open differential has the advantage of allowing the wheels to rotate at different speeds, which is suitable for normal conditions but becomes a disadvantage on less than ideal situations, such as driving on ice, snow and wet roads. 

A major shortcoming of this type is that if one tyre loses traction, the other tyre also experiences reduction in torque. It becomes very noticeable once the other tyre spins freely and does not get any traction at all. That's why you see cars getting stuck with one wheel spinning continuously with the other not spinning at all. To address this limitation, modern cars normally integrate traction control systems that apply brakes to the spinning wheel and make the torque available to the other wheel with traction. 

Locking Differential

The locking differential is a type where torque is transmitted to both wheels equally at all times. It is generally found in vehicles designed to traverse mud, snow, ice and other off-road conditions. Some models that have this type are the Jeep Wrangler, RAM 2500 Power Wagon and Mercedes-Benz G-Class. 

Locking differentials can be engaged or disengaged. When disengaged, this will work as an open differential. When locked, it shouldn't be used on high-grip surfaces like dry asphalt or concrete pavement as this may damage the gears when each tyre opposes the other, such as when manoeuvring turns or even slight curves.

Variations to this locking differential are available through car parts stores near you or online auto parts suppliers. Depending on the vehicle, numerous aftermarket systems are available like the air-locking differentials from ARB, Eaton locking gears that are electronically controlled or mechanical locking gears like the ones sold by Lokka. Aftermarket car parts like these often cater to off-road vehicles like the Toyota Hilux, Mitsubishi Pajero, Nissan Patrol and other popular makes and marques.

Limited Slip Differential (LSD)

A variation to the open differential, the limited-slip differential uses either a series of clutches and plates, viscous fluids or complex gear train in the differential housing which prevents the average amount of torque from transmitting to a slipping tyre. We can find this type in the Nissan 370Z with its sports package that uses viscous fluids, the Mazda Miata MX-5 and its series of clutches, and the Subaru BRZ with helical gears that activates the limited-slip function. Numerous high-end performance vehicles come equipped with electronically-controlled limited-slip differentials which are monitored and controlled by an on-board computer to determine if the driving situation calls for a locked or an open configuration. Electronic LSD can be found in cars like the Ferrari 488 GTB, BMW M3 & M4, Corvette Z51 and Cadillac CTS-V & ATS-V.

Under normal conditions, this differential acts like an open differential but engages during hard cornering or heavy acceleration which would typically cause a tyre to slip. This type is commonly found in race-oriented and high-performance cars and is also in some off-road vehicles.

Torque Vectoring Differential

The most advanced and most complicated type is the torque-vectoring differential. This system uses numerous sensors to detect road surface, throttle position, steering and other conditions that electronically activate internal clutches to engage gears within the differential housing.

It is mostly used in high-end, high-performance vehicles with rear-wheel drive, front-wheel drive and all-wheel drive. Some front-wheel-drive applications can be found on the Mercedes-Benz CLA and the Ford Focus. For all-wheel-drive cars, a good example can be seen on the Acura SH-AWD (Super-handling all-wheel drive). The Lexus RC F can be optioned with the rear-wheel-drive torque-vectoring system.

Welded / Spool Differential

The welded or spool differential is essentially the same as a locked differential but differs as the spools are permanently fused to transfer the torque directly to both wheels. It is commonly applied in race-only vehicles, like for drag racing and drifting competition cars.

This type is not advisable on cars used for the street because it can cause catastrophic failure to the gears inside the differential, which will be subject to constant stress, especially in turns and hard paved roads.

Maintenance and Parts

All forms of differentials need regular maintenance like other parts of a car. Oils or fluids used must be of the type recommended by the manufacturer. In the event of a breakdown in your car's differential, you may need to replace the whole assembly which you can buy either used or brand new. You may look up sellers near you through Carpart.com.au or send us a parts request, which we will send to all auto parts suppliers in Australia.

Fred Cajulis