How does it work? Is it electronic? I was wipping around a turn, next thing I knew it felt like both wheels kicked in and i was walking it sideways!!

 

operates using a bunch of clutch discs

when driving normally, the discs don't have any difference in speed relative to each other. so you are really driving around with 1 tire fire.

but when you get 1 tire spinning faster than the other tire, this causes the discs to spin and that friction generated causes them to grab and transmit power to the other tire.


since you were taking a turn, the outside tire was spinning faster than the inside tire...and that caused the discs to lock up with each other...was it wet outside?

here is a diagram of the Trac Loc Limited Slip your truck has

 

There he goes again! Tylus has the skinny on the things we want to know.

 

Oh, Tylus, my Swabbie friend, I must correct you on your limited slip description. To understand the limited slip, you must understand the open diff.

Open Differential

The standard, or open provides the baseline drivability situation we usually call “transparent” operation, because you seldom feel any signs that it’s working as designed.
First, the absolute rule. If you can get this straight in your mind, you will always understand how the differential works:

The average speed of both axles will always equal the speed of the ring gear.

If the ring gear is turning 100 rpm and the vehicle is going straight, both axles are turning 100 rpm. To get an average, add the two 100 rpm speeds and divide by two (100+100=200/2=100).
Engine torque enters the axle through the pinion shaft and gear and is transferred to the ring gear and differential case. The ratio of teeth between the ring and pinion provides the axle gear ratio, as well as changing the direction of torque flow. The differential case drives the pinion shaft. The pinion shaft drives the pinion gears (aka “spiders,” of which there can be two or four ) and the side gears, which are splined to the axles shafts, left and right. Assuming there is equal traction from both tires, the vehicle is going in a straight line and both tires are identical diameters, the pinion and side gears are driving the axles as a solid unit, with no rotation, or very little.
If you go around a corner, the side and pinion gears allow one axle to speed up and the other to slow down, but that speed change is proportional side to side. Torque is still being delivered to both axles but the pinion and side gears are in rotation inside the differential case.
As long as traction is equal on both tires, torque will flow equally to both. When traction is lost on one side, torque takes the path of least resistance and goes to the “loose” tire. That’s something we have all seen but still the absolute rule applies. In this situation, the pinions rotate around the stationary side gear and drive the other one. At 100 rpm ring gear speed, the high traction axle is at zero rpm while the other is running at roughly twice ring gear speed (0+200=200/2=100).

Limited Slip Differential

You’re stuck with an open diff, one wheel on a high traction surface and the other on ice. One wheel spins madly and the other is stationary. If you apply the brakes on that spinning wheel and slow it down, a percentage of the torque will be transferred to the side with traction (remember the absolute rule). That’s exactly what a limited slip differential (LSD) does. There are many mechanical ways to achieve that, from clutches to gears, but the amount of “braking” in a limited slip is measured by the torque bias ratio, or simply bias ratio. Many limited slips use the same types of pinion and side gears as an open diff, with clutches outboard of the side gears to apply braking.
With clutch type LSD, the amount of preload (preset braking) built into the clutches will dictate how many drivability issues there will be. A high bias ratio unit will have a lot of preload and vice versa. If the amount of preload (braking) exceeds the traction on one tire (such as the unloaded inner tire of a truck in a turn), the tire may lose grip and bark before the clutches reach their breakaway torque (the torque required to slip them).
With or without preload, the bias ratio is variable. As the torque load from traction increases inside the differential, gear separation forces push the side and pinion gears apart. If there is a clutch behind the side gear, those forces increase the pressure on them and the braking power. The opposite is also true. That’s why if you power around a turn with a LSD you increase the chance of barking tires, or sliding, and when you coast, you decrease them.
Factory LSD are usually low bias units, from about 1.6:1 to 2:1. That ensures no obnoxious drivability issues, such as chattering, tire barking in turns, etc. Aftermarket buyers usually want more traction and are willing to put up with more symptoms, so bias ratios usually start a little above 2:1 and go up to about 4:1. Some LSD can be tuned to go higher but at that point, it’s practically like a spool and an automatic locker will probably be closer to being transparent. At 2:1 the symptoms are minimal. They start being very noticeable at around 3:1. Overall, light rigs may exhibit symptoms sooner than large, heavy rigs. Gear type LSDs can usually get by with higher bias ratio without adverse symptoms than can a clutch style because they are not usually preloaded. An open diff, incidentally, has close to a 1:1 bias ratio.
The generic downsides of clutch type LSD are that the friction materials that provide the braking wear and the unit becomes less effective over time and miles. Depending on how you drive, there can be a serious degradation in bias ratio at between 50 and 100K miles. Also, most clutch type units require a friction modifier added to the oil to avoid clutch chatter. Most clutch type LSD can be rebuilt but some cannot. Gear type limited slips usually retain most of their factory bias ratio for their entire lifetime.
Finally, when the LSD is overcome on the trail, it can be enhanced by using brake pedal modulation or partially applying the parking brake. Partial application of the parking brake (assuming is applies on the rear wheels and not on the t-case as with some older rigs), will help equalize side to side traction even more. A little footbrake can do the same thing. Generally the parking brake is the better choice, because it applies only on the rear. Both these tricks will help with an open diff too!

 

ooo I see, I've put LSD in a car before, but now I know how it works! Thanks

 

Jim Allen, thank you for the lesson on LSD's. I knew how an open differential worked, but like Tylus, always thought the clutches kicked in somehow to help turn the axle with the least resistance instead of applying breaking force to the other side.