Limited Slip Differential vs. Traction Control/Brake Lock Differential

[Humvee4us]

I'm wondering how a LSD and traction control can go hand in hand on a Jeep? If a Jeep has LSD does traction control not work in that axle, or does traction control kick in before the LSD and therefore the LSD is pointless unless I completely turn off traction control?

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[Iggy]

Traction control is the "Brake Actuated Traction Control" (BTC) everyone is excited about. BTC has actually been around since open differentials were invented.

In an open differential, torque drives the right rear tire, generally. When that tire loses grip all the torque flows to that spinning tire until you run out of gas or a tire. Under the principle of torque flowing to the tire with the least traction, by gently applying the brake it will cause that spinning tire to stop spinning which would then causes the torque to flow to the other tire, the one that wasn't spinning. Now, both tires on that axle have an equal amount of resistance which causes the torque to flow to both tires simultaneously. Viola! Brake Actuated Traction Control.

So no, BTC isn't the same as limited slip or anti-spin. In those differentials, torque always goes to the tire with the most traction in a split fashion. Each differential will be a bit different and some can even be adjusted, but about 65% of the torque goes to the tire with the most traction and the rest goes to the other one. This can fluctuate nearly instantly based on which tire tase the most or least grip. In a locker, like what the Rubis have, torque is split equally and mechanically 50/50% left to right.

 

[entropy]

I'm wondering how a LSD and traction control can go hand in hand on a Jeep? If a Jeep has LSD does traction control not work in that axle, or does traction control kick in before the LSD and therefore the LSD is pointless unless I completely turn off traction control?

They work independently. BLD aids LSD.

 

[BCalvin]

Edit: wrong thread.

 

[aldo98229]

JLs with LSD also come with BLD, just like any another JL. They are separate systems.

Here’s one simplified way to think of the two:

• BLD reduces torque to a spinning wheel in the hope of regaining traction
• LSD distributes 80% of available torque to the wheel with the greatest traction

 

[Boatbuilder88]

Trac-Lok anti-spin (limited slip differential) is always active and works independently of Brake Lock Differential.

Brake Lock Differential works with both axles but is only active in 4-Hi and 4-Lo. BLD will kick in if the torque bias is higher than Trac-Lok can handle.

 

[Uhdinator]

BLD works in all modes.........2WD, 4H, 4L

 

[entropy]

BLD works in all modes.........2WD, 4H, 4L

No it doesnt. LSD works in all modes. BLD only works kn 4H,4LO.

 

[Badweissenbier]

I was thinking bld is disabled in 4lo. I know it is on a rubi.
Edit that’s where lsd comes into play

 

[jeepoch]

Brake Limited Differential (BLD) is enabled all of the time independent of transfer case position. Please see my latest research on this subject within the 2H-vs-4H thread.

https://www.jlwranglerforums.com/forum/threads/2h-vs-4h.59924/page-6#post-1335250

[Edit]
Also found this article from an FCA Active Control Systems Engineer:
https://blog.fcanorthamerica.com/2008/02/11/jeep-brake-traction-control-explained/

It does indeed seem to imply that BLD is only enabled in 4wd modes. However, he somewhat contradicts himself by saying BLD is active anytime Electronic Stability Control (ESC) is. And that BLD remains active when you disable ESC with a single push of the ESC-Off pushbutton.

According to the owner's manual, ESC is active in both 2Hi and 4Hi (unless placed in a reduced mode) and is automatically disabled in 4Lo.

So it will take some further experimentation now to answer this question precisely. Our available documentation is contradictory and confusing at best

Jay

 

[entropy]

Brake Limited Differential (BLD) is enabled all of the time independent of transfer case position. Please see my latest research on this subject within the 2H-vs-4H thread.

https://www.jlwranglerforums.com/forum/threads/2h-vs-4h.59924/page-6#post-1335250

Jay

There is a video from Jeep explaining how it all works, came out in 2018. BLD is only active in 4H and 4LO, while LSD is always active because it is mechanical. But that video could be wrong. I dont think BLD would be good on regular driving conditions, it is kinda clunky.

 

[jjandascog]

In an open differential, torque drives the right rear tire, generally. When that tire loses grip all the torque flows to that spinning tire until you run out of gas or a tire.

The same amount of TORQUE is delivered to both tires all the time ALWAYS in a type differential.

It is HORSEPOWER (rate of work) that is not delivered equally depending on conditions.

 

[TheRaven]

Couple of things:

- BLD is on ALL THE TIME regardless of drive mode, gear, or diff type. It cannot be turned off. If you have an LSD or you have your diffs locked, it will not operate simply because it never senses a need to. This is stated in your manual.

- Open diffs do not "only drive one wheel". This is a very pervasive but completely incorrect notion that won't go away. As long as both wheels have traction, both wheels are driven. It's when one wheel starts to lose traction that problems arise, because the less traction a wheel has, the more power it gets.

 

[entropy]

Couple of things:

- BLD is on ALL THE TIME regardless of drive mode, gear, or diff type. It cannot be turned off. If you have an LSD or you have your diffs locked, it will not operate simply because it never senses a need to. This is stated in your manual.

- Open diffs do not "only drive one wheel". This is a very pervasive but completely incorrect notion that won't go away. As long as both wheels have traction, both wheels are driven. It's when one wheel starts to lose traction that problems arise, because the less traction a wheel has, the more power it gets.

1:47. I guess this video is wrong then? "BLD is a feature of traction control, active in 4H and 4LO". Being a feature of traction control doesn't mean it is active whenever traction control is active.

If you want to avoid wheel spin on 2WD you need an LSD, that's mostly what they're for. It is very clear from the video.

 

[TheRaven]

1:47. I guess this video is wrong then? "BLD is a feature of traction control, active in 4H and 4LO". Being a feature of traction control doesn't mean it is active whenever traction control is active.

If you want to avoid wheel spin on 2WD you need an LSD, that's mostly what they're for. It is very clear from the video.

Yes that video is wrong - and weirdly worded.

BLD cannot be turned off. It's also not some super-advanced Jeep thing. It's pretty standard issue these days...pretty much any vehicle that does not have a more sophisticated traction management system that always operates will have a variation of BLD that is always watching.

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