Exactly what is the point of a "Limited slip" rear end?

[bwright1818]

This winter, I purposfully parked one rear wheel on dry pavement and the other rear wheel on a frozen puddle. The wheel on the puddle slipped like crazy when I tried to move. This summer, I was putting on my summer wheels and just for the heck of it, while one rear wheel was up off the ground, I carefully engaged first gear and let up the clutch. The wheel off the ground just spum aimlessly. I increased the engine RPM to as much as 1500 and it still just spun and didn't even remotely try to knock the car off the jack. I spent the extra $$$ for the limited slip option. It is right on my as delivered build sheet. During the winter, I had actually got stuck in about 6 inches of snow, even in 4x4. My opinion is that this is one candy-ass Jeep that doesn't deserve to wear the name. What am I not understanding? Do you have to red line the engine before the limited slip starts to function?

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[MEHillwalker80]

Put your VIN in the below link to see if you really did get the LSD.

https://fcacommunity.force.com/RAM/s/equipment-listing

 

[Dan M.]

Sounds like it isn't working or you didn't actually get it to me.

 

[Joe98]

Interesting

 

[TheBirdie72]

Sounds like you got the unlimited slip rear end by mistake.

 

[azwjowner]

How to tell if you have a LSD:

Sounds normal to me. A LSD directs a multiple of the torque on the lowest traction wheel to the other wheel; it's not a locker. If one wheel has completely zero traction, a LSD won't do anything because even 3 times 0 is 0. In cases where one wheel has very low traction, that's where it works because it transfers some multiple of that low traction torque to the other wheel, allowing the Jeep to move based on that other wheel (whereas an open differential would not send any more torque to the other wheel, so both wheels are limited to the lowest traction of the two wheels).

Someone also could have added too much friction modifier to the diff oil so that the clutches in the LSD aren't ever grabbing.

 

[Valpo Jeep]

A limited slip diff will still spin just 1 wheel in very low traction situations as you have experienced. It will try to apply torque to both wheels but still only spin 1 on ice if the tire breaks free.

 

[Xcoaste]

The clutches can wear out eventually.

 

[mwilk012]

Sounds like you have a bad differential. Try changing the fluid and see how bad it looks.

I’m not 100% sure if the manuals have it or not, but I am fairly positive that you should also have BLD helping you out there and that isn’t happening in your case. Not good.

 

[Mocopo]

Try to feather the breaks just a tad at the same time. Add some friction. I understand what others are saying that this might be normal, but my LSD in my JK was top notch, would have rolled me right out of the situations you're describing.

 

[Jank4AU]

I was fairly certain to officially engage LSD you had to apply slight brake pressure as noted by @Mocopo above. Or at least if you have a completely free spinning wheel.

 

[aldo98229]

Yes, it is extremely rare that in real life one rear wheel will have zero traction. The only situation I can think of is if you are at full articulation and have one tire completely off the ground. In that case, feathering the brakes will force the LSD to “lock” up.

 

[oldcjguy]

Limited slip diffs work using clutches in the diff, but they still require some resistance the wheel with the least amount of traction for it to work efficiently. When in 4wd you can apply the brakes while applying the gas. That will help transfer the torque to the wheels with more traction. Since you are in 4wd the brakes won't stop you or cause more loss of traction.

Here's how a limited slip works if you're interested:
Inside your differential is the "carrier". the carrier is what your ring gear is mounted to. Inside the carrier are 4 "spider gears". each axle goes through a spider gear on the side of the carrier. Those spider gears mesh with the other 2 spider gears that are connected to the carrier itself. All 4 spider gears are meshed together. This gear meshing is what allows the rear to "differentiate" or allow one axle to spin faster than the other. We need this because when a vehicle goes through a turn the inside wheel is actually travelling a shorter distance than the outside wheel, so the outside wheel must turn faster to keep up. The spider gears rotate inside the carrier allowing one wheel to spin faster than the other. When going in a straight line the spider gears don't rotate inside the carrier and both axles spin at the same speed. The problem with this design is as power is being applied the wheel with the least amount of traction will break free and start spinning faster than the other. As the engine revs up that wheel spins faster and the wheel with the most traction sits there. That's what happens in an open diff.
Enter the limited slip diff. Limited slip diffs have clutches and "steels" in the diff. The steels are splined to the axle and the clutches are splined or mounted to the carrier. The steels cannot rotate on the axle and the clutches can't rotate in the carrier. These are put together in a "clutch pack" A clutch pack is alternating steel disks and clutch disks. They are all between the inside edge of the carrier and the spider gear the axle is splined into. Picture them being in there kind of like washers between the carrier and the spider gear. So when one axle spins faster than the other the spider gear rotates inside the carrier case. The steels spin with the axle and the spider gear while the clutch disks stay stationary to the carrier. the friction between the steels and the clutch disks tries to stop the spider gear from spinning in the carrier thus transferring that force to the other axle (trying to keep both axles going the same speed). Just sitting there there is not much force squeezing these disks and steels together to make friction. The spider gears are shaped kind of like cones. Because of their shape (and physics) when the spider gears are under a load (trying to turn or move the vehicle applies tremendous force) they are always pushing away from each other. Well that pushing away pushes the side spider gears (the ones splined to the axles) out against the carrier case itself. When there are clutch packs between the case and the gear they get squeezed together. This is called the dynamic load. On dirt, concrete and asphalt both wheel on an axle have a lot of friction so a lot of force can be pushed into the clutches and steels. On the street the jeep with a limited slip will do 2 wheel burnout. One without will probably do a one wheel burnout. Even with limited slip you can easily maneuver through tight turns because you're likely not on the gas so not applying a load to the gears. The clutches and steels happily slip. This is where LSD has an advantage over a locked diff. With a locked diff the axles are locked together and you are dragging one wheel through a turn or they are trying to push the jeep straight.

With one wheel on ice or in the air there is very little to no friction on one wheel so not much force can be applied to the clutches and steels. That's why you can still get stuck. By applying the brakes you are creating false friction on the wheel on ice which puts that load on the clutches so power can be transferred to the other wheel. This is what the BLD or "Brake Lock Differentials" do. The computer can actively engage individual brake calipers to help create false traction. Obviously when you do it with your foot and the brake pedal you have to be in 4wd or the front brakes will stop the front wheels from moving and try to prevent the jeep from moving.

Google "How limited slip differentials work" for some good animations.

 

[LuvHydro]

It was my understanding that Wranglers had a pseudo LSD in that it automatically applied brakes to the slipping wheel?

 

[Jtclayton612]

It was my understanding that Wranglers had a pseudo LSD in that it automatically applied brakes to the slipping wheel?

it sometimes takes quite a bit of time and wheel speed for the BLD to kick in.

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