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Limited Slip Differential vs. Traction Control/Brake Lock Differential

BRuby

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1 TCS monitors the amount of wheel spin of each of the driven wheels

2 A feature of the TCS is BLD which functions similarly to a LSD

3 BLD may remain enabled even if TCS and ESC are in reduced modes

4 When in Partial Off mode the TCS will be disabled except for the LS feature. Also the engine power reduction feature is disabled and EVS is reduced

5 When the ESC off button is held for 5 seconds while the vehicle is stopped the TC and SC will turn off

So it seems that BLD is active in 2Hi 4Hi 4Lo and when rear lockers are engaged. BLD should turn off when the ESC button is held for 5 sec - as well when both lockers are engaged.

In our exp we find that 4Hi with ESC on provides amazing traction on snow and ice covered roadways using stock KO2s. But uphill bends on ice can induce understeer which is controlled by letting off the go pedal. It seems the proper nannies kick in to get the JL back on the intended track. Has happened a couple times due to a touch more speed than the KO2s could handle.

Off-road what helps to get unstuck is to turn on both lockers and churn away. Even then that can be futile and shovels and ramps are required. Chains as a last resort before getting pulled out. Deep slush with ice under can be a wicked combo to overcome. Looks ok but once in it you are stuck up to your axle. Have seen 5+ completely stuck this season requiring a tow truck to extract.

And yeah if something like a Torsen was available vs clutch based - we would probs get that with a manual Ox up front. We do go off-road but our main use scenario with this JL is to get up resort mtn roads for skiing SB. For us Rubi FTW.

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entropy

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1 TCS monitors the amount of wheel spin of each of the driven wheels

2 A feature of the TCS is BLD which functions similarly to a LSD

3 BLD may remain enabled even if TCS and ESC are in reduced modes

4 When in Partial Off mode the TCS will be disabled except for the LS feature. Also the engine power reduction feature is disabled and EVS is reduced

5 When the ESC off button is held for 5 seconds while the vehicle is stopped the TC and SC will turn off

So it seems that BLD is active in 2Hi 4Hi 4Lo and when rear lockers are engaged. BLD should turn off when the ESC button is held for 5 sec - as well when both lockers are engaged.

In our exp we find that 4Hi with ESC on provides amazing traction on snow and ice covered roadways using stock KO2s. But uphill bends on ice can induce understeer which is controlled by letting off the go pedal. It seems the proper nannies kick in to get the JL back on the intended track. Has happened a couple times due to a touch more speed than the KO2s could handle.

Off-road what helps to get unstuck is to turn on both lockers and churn away. Even then that can be futile and shovels and ramps are required. Chains as a last resort before getting pulled out. Deep slush with ice under can be a wicked combo to overcome. Looks ok but once in it you are stuck up to your axle. Have seen 5+ completely stuck this season requiring a tow truck to extract.

And yeah if something like a Torsen was available vs clutch based - we would probs get that with a manual Ox up front. We do go off-road but our main use scenario with this JL is to get up resort mtn roads for skiing SB. For us Rubi FTW.

57207D12-22EF-42E4-A14C-CBCE4CA19D81.png


BB35EA30-4D0E-4C9A-B100-87E12F0B97A1.png


9D2A0CBA-5584-41C6-A20D-8D898727EAE7.png
How do you conclude BLD is on when on 2H?
 

txj2go

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Well after 20-30k miles it won't matter cuz the POS LSD that Jeep uses will be toast.
I've worked on cars with limited slip where the limited slip was not so limited. I don't know if the clutches wear or the springs weaken, but the result is that they can't offer much resistance to one side spinning freely.

How do you conclude BLD is on when on 2H?
In 2H put one rear tire on dry pavement, the other rear tire on ice. Apply some throttle and see what happens.
 

BRuby

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How do you conclude BLD is on when on 2H?
1 ESC is turned on by default when you start the JL
2 Often times 2H will be engaged but 4Hi is ok too
3 TCS works with ESC
4 BLD is a feature of TCS
5 FCA notes when TCS and ESC can be turned off
6 FCA notes when BLD stays on but TC turns off

In what circumstance do you see FCA turning off TCS or BLD or ESC in 2Hi so long as you do not touch the ESC off button?

What would be useful is for you or anyone to contact FCA and simply ask their design engineers and get an answer in writing from them. Is BLD on in 2Hi?

Aside from that why would FCA enable BLD in 4Hi but not use that feature in 2Hi? We can only go by our seat of the pants testing but ESC and TCS (plus its feature BLD) seem to be on in 2Hi. It would be idiotic not to engage TC and BLD while ESC is on. But who knows with Fiat. So yes the vid may be misleading as others have noted. FCA should however clarify this in their most current owners manual. But probs will not happen.

EDIT: For those unaware of JL options this vid shows what 4Lo gives you without lockers - then with rear locked (or sim to LSD locked up) - then with F+R locked. Front lockers are key to help pull you out or up.

 
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TheRaven

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EDIT: For those unaware of JL options this vid shows what 4Lo gives you without lockers - then with rear locked (or sim to LSD locked up) - then with F+R locked. Front lockers are key to help pull you out or up.

That video could not have been done more poorly. For the first two tests he got the Jeep completely on the slope, then STOPPED, then gave it just enough power to spin a wheel, then gave up. Why? Why not show what it takes to get to the top in each setup? He never even gave the system a chance to work. The worst part is he never stopped in either attempt with both axles locked. He would have had wheelspin in every single scenario if he did it correctly.
 

Uhdinator

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That video could not have been done more poorly. For the first two tests he got the Jeep completely on the slope, then STOPPED, then gave it just enough power to spin a wheel, then gave up. Why? Why not show what it takes to get to the top in each setup? He never even gave the system a chance to work. The worst part is he never stopped in either attempt with both axles locked. He would have had wheelspin in every single scenario if he did it correctly.
I've gone up an incline like that but longer and a little steeper in my 2Dr Sport and didn't spin a tire. You don't need lockers to do something like this. (yea he got a run for it with the lockers 🙄)
 

BRuby

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Yeah not a perfect test by any stretch and anyone can criticize his vid. But super easy to replicate in snow, slush, or ice if you wanted to test yourself. At least he made a vid and posted it. Tons of other vids showing locker off vs locker on differences - in all types of conditions. Rock climbing, sand, mud, snow, whatever. Just google.

EDIT: Just back from SB. Pressing ESC off when in 2Hi pops up Traction Control Off in the dash display. As well there is a distinct difference on ice when TC is off vs on.

As noted tons of other vids are available. If not happy with his content send him a comment and post your own vid.
 
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TheRaven

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Yeah not a perfect test by any stretch and anyone can criticize his vid. But super easy to replicate in snow, slush, or ice if you wanted to test yourself. At least he made a vid and posted it.
That video doesn't show anything at all.

And you are correct, there are tons of videos out there showing what these Wranglers can do, with and without lockers.
 

Uhdinator

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Just tested today in 2WD. Traction control on. Right side on frozen sand/gravel. Left side on hard packed snow/ice......stopped, gave it gas, TC lights flashing, engine power reduced not much spin on the ice. No prob moving.

TC Off......stomped gas, TC lights flashing, left wheel spinning and gradually slowed while accelerating......was moving the whole time and had no prob moving from the start, just more wheel spin at first without the engine power reduction. Looks to me like it works fine in 2WD.
 

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word302

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Just tested today in 2WD. Traction control on. Right side on frozen sand/gravel. Left side on hard packed snow/ice......stopped, gave it gas, TC lights flashing, engine power reduced not much spin on the ice. No prob moving.

TC Off......stomped gas, TC lights flashing, left wheel spinning and gradually slowed while accelerating......was moving the whole time and had no prob moving from the start, just more wheel spin at first without the engine power reduction. Looks to me like it works fine in 2WD.
It definitely does.
 

jimcoffey62

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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
Close, but not quite accurate.
An open differential applies equal torque to both wheels. If one wheel has zero traction it takes essentially zero torque to make it spin = the same zero torque is going to the other wheel. And since that's not enough torque to get you moving you don't move.

so, BLD applies braking force to the spinning wheel. And it now takes more torque to make it spin. Since the open dif applies equal torque to both wheels, the non spinning wheel gets some torque.... the same amount of torque that the brake is holding.

But if you do the math you only get 1/2 the available torque from your engine, Because
1/2 of the torque is going to the spinning wheel, and the brake is holding it stopped
so 1/2 of the torque can go to the wheel with traction.

aka If it takes 100 ft lbs of torque to get your jeep moving....
The engine applies 200 ft lbs total to the axle of which - 100 ft lbs goes to the spinning wheel but the brakes clamp it with -100 ft lbs
And the same 100 ft lbs go to the wheel with traction and you start moving.
But it required a total of 200 ft lbs from the engine to the axle.

In 4 low you typically have PLENTY of torque so this works well.
 

Flatties 4ever

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I run a Nitro Helix (lsd) in the rear and always turn off TCS “when a more spirited driving experience is desired” (rooster tails, drifting and donuts)
 

Squibbles

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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.
Horsepower is a function of torque, 550 ft pounds a second is 1 horsepower
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