Limited Slip Differential, or LSD, is a type of axle gearing that allows both wheels sharing an axel to lock up and spin at the same time when one wheel starts to slip. For this reason, limited slip differentials allow power to be transferred to the wheel with the most traction. LSD maximizes traction and makes controlling oversteer easier like when drifting. LSD is essential to building a drift car.
Advantages of limited slip differential include less inside wheelspin when accelerating out of a tight corner and more horsepower to the ground. Suspension tuning is needed to gain all the benefits of a limited slip differential. In drift cars, coil over damper kits and pillow ball upper mounts for camber correction are typically the suspension choice.
The two main types of limited slip differentials are torque sensitive mechanical LSDs like clutch and geared based LSDs, and speed sensitive hydraulically controlled LSDs like viscous and gerotor pump LSDs.
Clutch type limited slip differentials respond to driveshaft torque. The more driveshaft torque present, the harder the clutches are pressed together and the more closely the drive wheels are coupled to each other. Torque-sensitive geared mechanical limited slip differentials utilize worm gears to detect torque and lock the wheels accordingly. Geared LSDs are dependent on torque, not the speed difference between wheels.
Viscous limited slip differentials use silicone-based hydraulic oils and stacks of interlocking (but non-touching) perforated discs to lock the differential. Half of the discs are connected to the inner driveshaft and the other half is connected to the outer differential carrier. When under the stress the high torque, the hydraulic oil thickens and fills the gap between the discs effectively locking the discs together and locking the differential.
Gerotor pumps work by hydraulically compressing a clutch pack. When one wheel starts to slip, the pump pressurizes hydraulic fluid into the clutch pack area providing frictional resistance that transfers torque to the wheel with traction.
There are also electronic limited slip differential systems that use anti-lock brake sensors to electronically monitor wheel speed. If one of the wheels begins to rotate faster than the other, the computer briefly applies the brake to that wheel.
A locking differential, or locker, is often used in off-road 4WD vehicles. In the default setting, both wheels are locked. A selectable locker is typically used by street cars that also drag race. On the street, the car would use the open differential setting and later be locked at the drag strip by compressed air, a cable, electric actuator, or hydraulic fluid locking mechanism.
If you want to know if your car has LSD, here is how to find out. Do a burnout and see if your car left one or two tire marks. 2 tire marks = LSD. If you know your car has a limited slip differential and it only leaves one tire mark, the LSD may need to be serviced or replaced.
November 11th, 2007 by Tom
Filed under: Car Parts