The Differences Between Differentials

Differentials limit the loss of torque to a slipping wheel through clutches and gears

Often times when driving down a logging road you encounter mud on one side of the road. You slow down and travel through it, only to find you are losing traction on the muddy side and the wheel starts to spin. Before you know it, you are stuck on what appears to be a basic road. Why? It all comes down to the differential, and I’m not talking about math but the differential on your vehicle’s axle.

A standard differential, what is often referred to as an ‘open diff,’ is what comes from the factory with most new trucks. The open diff holds the ring gear and a set of gears called spider gears. These spider gears are responsible for allowing a vehicle to negotiate a turn and allow the outside wheel to travel farther and turn faster than the inside wheel.

This type of open design works great for most of the pickup trucks on the road today.

However, when a truck with an open differential meets loose gravel, or a wet section of the road, it directs power to the wheel with the least amount of resistance. The result is the wheel on the loose surface spins free, while the wheel on the better traction surface provides little or no power.

Limited slip differentials are designed to “limit” the tendency of an open diff, and send power to a wheel that lacks traction by redirecting the power to the other wheel. A limited slip diff sends power to both wheels equally when travelling straight, and when one wheel spins due to a lack of traction, the differential will automatically provide torque to the other wheel with traction.

These differentials limit the loss of torque to a slipping wheel through clutches, gears, and other methods, depending on the unit.

It will not provide 100-per-cent lock up of the differential in extreme situations, such as when a wheel completely loses traction. Limited slips are recommended for daily driven vehicles and are used in many applications where traction is sometimes needed. They are also ideal for front axles of 4x4 vehicles that are not equipped with front hubs that can be disengaged. A locking differential, or ‘Locker,’ uses a mechanism that allows left and right wheels to “lock” to each other and turn at the same speed regardless of which axle has traction or how little traction a slipping wheel has.

This means traction can be sent to a wheel that may be planted firmly on the ground while the other wheel of the axle is completely off the ground. In this situation an open differential will spin the free wheel, sending absolutely no torque to the wheel in the ground. A limited slip in this situation will send some torque to the wheel on the ground but possibly not enough to provide any forward momentum.

Article written by: Ian Harwood - "The Truck Guy"
Corporate Sales and Operations Manager for Custom Truck Parts