Understanding LSD, past & current.

[Flip]

In the past I had read and watched a lot of videos regarding limited slip differentials. The complaint was basically if one wheel went off the ground, all of the power tranferred to that wheel and that one wheel in the air would just spin.
In this video, it says the power is transferred to the wheel that is getting more traction. So, this has changed over the years, yes?

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[PunksJL]

You are referring to an open differential (not a limited slip) in your example where the tire with no traction spins. Limited slip will provide traction to the wheel with traction. There are various ways of doing this including internal mechanisms within the differential (including lockers) and of course modern-day traction control systems use brake modulation to get the wheel with traction to spin and move the vehicle. I used to have an old Ford that has a Trac-Lok rear diff. It was basically an open diff but if you pressed on the emergency brake pedal (yes, they used to have pedals for emergency brakes) it would transfer some of the power to the not slipping wheel.

 

[Jeep Wick]

In the past I had read and watched a lot of videos regarding limited slip differentials. The complaint was basically if one wheel went off the ground, all of the power tranferred to that wheel and that one wheel in the air would just spin.
In this video, it says the power is transferred to the wheel that is getting more traction. So, this has changed over the years, yes?

I know the helical limited slips say you just tap the brakes if it lifts a wheel. I don't think that applies to a 'traditional' LS diff.

 

[58Willys]

You are referring to an open differential (not a limited slip) in your example where the tire with no traction spins. Limited slip will provide traction to the wheel with traction. There are various ways of doing this including internal mechanisms within the differential (including lockers) and of course modern-day traction control systems use brake modulation to get the wheel with traction to spin and move the vehicle. I used to have an old Ford that has a Trac-Lok rear diff. It was basically an open diff but if you pressed on the emergency brake pedal (yes, they used to have pedals for emergency brakes) it would transfer some of the power to the not slipping wheel.

Although totally different systems, the Jeep brake lock differential system and the old trac-lock; work in a very similar manner.

OP - There are many flavors of limited slip/posi-traction etc…; but open and limited slip are the same as they have always been. Punks is correct in what you were describing being a limited slip. An open diff will spin the wheel with less traction.

 

[Flip]

My old brain is stuck in the past. I keep thinking of the jeep videos where one wheel went off the ground and the tire would spin. Essentially making what I think they used to call true trac or something like that, it didn't seem to work very well in those situations. New technology, transferring the power to the wheel on the ground, is a lot better I think.

 

[Flip]

I was having a conversation with @Tredsdert about LSD. He was trying to explain it to me but again I kept thinking of much older technology. When he mentioned new technology, that got me thinking and I found a few videos. This was very new to me. He was right and I was wrong.

Thank you treds for being patient with me.

Thank you everyone for explaining for me. I think I have a better understanding of it now.

 

[grimmjeeper]

I know the helical limited slips say you just tap the brakes if it lifts a wheel. I don't think that applies to a 'traditional' LS diff.

It does. Same applies to an open diff. The effectiveness is based on just how much torque bias there is.

Thing is, when you hit the brake pedal you apply brakes at all 4 cornes. And that adds even more resistance to the tires that aren't spinning, limiting how effective the technique is.

The BLD system uses the ABS module to apply the brake only to the spinning wheel, leaving the brakes off for the rest of the wheels. This is a more effective way to get the energy to the wheel with grip. But again, it isn't 100% effective.



All limited slips do just what they say. They limit slip of a wheel with no traction. Doesn't matter between helical gears or clutch packs. Different mechanism, same result. But the key word is "limit". They don't eliminate slip. They only reduce it. Lift a tire and they will end up letting it free spin.

 

[PunksJL]

Modern technology has really raised the bar on off road performance. This is is interesting comparison between a basic Wrangler 2-door without lockers and a new 2025 4-Runner. The little Wrangler is just using open diffs but the computer is modulating the brakes with such effectiveness the performance through the snow is pretty impressive.

 

[2nd 392]

I was having a conversation with @Tredsdert about LSD. He was trying to explain it to me but again I kept thinking of much older technology. When he mentioned new technology, that got me thinking and I found a few videos. This was very new to me. He was right and I was wrong.

Thank you treds for being patient with me.

Thank you everyone for explaining for me. I think I have a better understanding of it now.

I reiterate to unstick your brain, a true LSD functions the same as they always have, automatically providing power to both wheels when one has traction loss, less effective but similar to a locker. The newer tech is the BLD type that require your input to function. I don’t like LSD in the front because you can’t turn it off.

 

[Flip]

I reiterate to unstick your brain, a true LSD functions the same as they always have, automatically providing power to both wheels when one has traction loss similar to a locker. The newer tech is the BLD type that require your input to function. I don’t like LSD in the front because you can’t turn it off.

What is BLD?

 

[grimmjeeper]

I reiterate to unstick your brain, a true LSD functions the same as they always have, automatically providing power to both wheels when one has traction loss similar to a locker. The newer tech is the BLD type that require your input to function. I don’t like LSD in the front because you can’t turn it off.

I've never had trouble with limited slip in the front. You typically put one with lower torque bias in the front.

I had an XJ with TrueTracs front and rear. That thing was unstoppable in the snow and great to drive in all conditions.

 

[grimmjeeper]

What is BLD?

Brake Lock Differential.

That's Jeep's brand name for their computerized traction control.

 

[2nd 392]

What is BLD?

Brake lock systems as previously described.

 

[2nd 392]

I've never had trouble with limited slip in the front. You typically put one with lower torque bias in the front.

I had an XJ with TrueTracs front and rear. That thing was unstoppable in the snow and great to drive in all conditions.

I have, my 89 Bronco’s steering was diminished in heavy snow or mud just as my 63 Jeep with mechanical lockers. I did learn that unlocking a hub was helpful, so it didn’t tend to plow straight ahead regardless of how the wheels were pointed, sometimes at a forward momentum loss. Selectable lockers for the win.

 

[AdamG]

I've never had trouble with limited slip in the front. You typically put one with lower torque bias in the front.

I had an XJ with TrueTracs front and rear. That thing was unstoppable in the snow and great to drive in all conditions.

Have them in my 2dr and they are great.

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