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Differentials Explained - Limited Slip Differentials LSD

An article explaining the different forms of limited slip differentials
A limited slip differential, or LSD, is designed to transmit usable power between the drive wheels of your vehicle when loss of traction occurs. While driving in a straight line, power transfer will usually be an even split between tires. As one wheel loses traction, the LSD unit will automatically transfer power to the wheel to the other wheel. Generally the power split is only about 30% of the available power to the wheel with traction. This is much better than 0% however as in a standard open differential unit. The automatic design eases vehicle on road drivability and makes these types of units more desirable for daily driven vehicles.

The standard type of limited slip differentials utilize an internal pack of clutch discs. Different manufacturers will use different amounts and thicknesses of discs. These discs are located behind the spider gears (or equivalent depending on the unit's design). The clutches are held in place by a series of tension springs, or a single, large high tension spring. As one wheel loses traction, the spring tension increases on the clutch discs and prevent the spider gears side from excessive spinning. The engine power must now flow through the path to the wheel with traction, giving the vehicle more available power needed to generate forward momentum.

Standard clutch pack units require a very strict maintenance schedule.  Pack rebuilds are needed at various mileage intervals, and the addition of additives into the gear fluids is also a must.  Without these additives the clutch disc would be unable to provide proper friction, and render the unit useless.
An alternate choice for a LSD unit is the Detroit TrueTrac. This unit is very popular due to its 100% mechanical design. This means there aren't any clutch disks, and the routine maintenance they require is nullified. The TrueTrac's internal design separates it from standard units through the use of planetary helical gears. This provides smooth and quiet operation while power is transferred between the wheels.

Under normal driving conditions, the TrueTrac will remain in an unlocked, almost open differential like state. Once the tires require addition traction, the unit engages automatically, and the torque split will be 3.5 times higher on the wheel with traction. This is a significantly greater power transfer and increase over the standard clutch disc design.
Article Type: 
How It Works