ARE THEY ALL THE SAME?

No, there are different types of LSD, with some types being more suitable for use in certain disciplines.

First up are automatic torque sensing differentials such as the Quaife ATB unit. These differentials bias torque to the driven wheel with most grip. Extremely durable and smooth in operation, an ATB type is ideal for performance motoring; whether it be on road or track. It replaces the standard ‘open’ differential, is a ‘fit and forget’ product and doesn’t require any special maintenance.

Next up are plate-type differentials. These are most popular in rallying (and for rear-wheel drive hooliganism!) where there are often loose surfaces to contend with. Plate-type LSDs lock once a loss of traction is detected; for instance, if one driven wheel is in the air, drive is maintained. Harsher in operation than torque biasing differentials, plate-type LSDs also require regular maintenance, including the replacement of the differential’s clutch plates.

The final form of LSD is the viscous differential. These were commonplace on fast Fords throughout the ’80s and ’90s, but have since been phased out as Ford has tended to fit ATBs on more recent performance models. A viscous LSD relies on something called hydrodynamic friction from fluids with high viscosity – imagine walking through water, its easy to do slowly but trying running in water you meet a lot of resistance. Now imagine doing that in a vat of treacle and you can see how the hydrodynamic friction effect can be used to resist, or limit, the slip of one wheel. Viscous differentials are compliant and easy to use, if not generally less efficient than mechanical types as some of the power can be lost during its operation.