Brake Lock Differential (BLD) techniques for open diff (non-locker & non-LSD) JLs

[AcesandEights]

I think you think it isn't engaging because it probably isn't. You're probably not applying steady, even throttle because it's slipping, thinking you need to let off the throttle, or apply brake. The opposite is true. That's when you need to increase throttle slightly, until it engages. You'll hear it, as you maintain throttle it'll start to make nasty braking sounds, and then the other wheel will start to turn.

I will say, it seems counter-intuitive, but don't let up on the throttle or apply brake, because that defeats BLD

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[entropy]

BLD is all about automation. It is an electronic system that does exactly that. It applies the brakes to the spinning wheel automatically to send torque to the one with traction.

There are no tricks. The tricks are if you don't have BLD. It is not a locker so don't expect that much from it. And when it engages it is for very short bursts of time.

 

[Htfan]

Sure, but what makes you think/believe it isn't working without your need to depress the brake pedal? I ask because your saying you need to do so essentially defeats BLD.

I had someone with me outside the vehicle watching the wheels. We tested both with and without applying brake.

Is it possible, you're talking about ESC? Not BLD. My understanding is ESC applies the brake automatically when wheel slippage is detected.

 

[BDinTX]

Hey it’s not “simple” pressing the locker button! You have to put down the Starbucks coffee and take your eyes off the parking lot to look where you’re stabbing your finger. If you’re not careful you accidentally push Aux 1 turning on all the light bars and blind mall security or hit a curb…

 

[AcesandEights]

@Htfan No, read the Stellantis blog I posted. BLD works by applying brake, automatically, to individual wheels. If you apply brake, you defeat BLD. You must apply throttle for BLD to have enough torque transfer, and to try to maintain the same speed of the wheels.

 

[Htfan]

@Htfan No, read the Stellantis blog I posted. BLD works by applying brake, automatically, to individual wheels. If you apply brake, you defeat BLD. You must apply throttle for BLD to have enough torque transfer, and to try to maintain the same speed of the wheels.

If this is the case, sounds like I may need a trip to the dealership because it's clearly not working on my JLU.

 

[AcesandEights]

That may be the case.

 

[jludave]

Is it possible, you're talking about ESC? Not BLD. My understanding is ESC applies the brake automatically when wheel slippage is detected.

No. I know the difference.

 

[Bzinsky]

This is how most open diff awd systems control the diffs.

The science makes sense, but every time you see some sort of off road test using these systems, they don’t really work. They all struggle to apply power to the wheel that needs it. I have not seen one off road test where open diffs that mimic limited slip/lockers using the brakes has functioned as it should in theory. Especially when the going gets tough and one side has very little traction. These also never work as they should in the dry.

Why this is, I’m not sure.

Taking at stab at why…

-imagine you’re in your jeep in 4wd, two tires with very limited traction, not in the air, but close to it. You have tire in the front with traction, and one in the back. Well then when the computer tries to apply the brakes to the two tires that has limited traction. So does this mean you are only sending power to the tires with traction? No, it means your now sending equal power to all 4 tires. Why is this different than locked diffs? Because the brakes are on two of the wheels! You can’t send anywhere close to your full power to these driven wheels. Your hp gets taken away by the brakes, combined with the fact that the ecu is likely limiting engine output in this scenario. Then it’s just a balancing act for the computers for more or less braking and more or less hp. What happens is they just sit there with strange surges in power and it seems like the car is just trying to process what’s going on.

I’ve never seen it work well.

TFL has some really good tests of these where they compare stock vehicles going up their mountain trails. It’s pretty much how every awd and open diff 4wd system works. The actual lockers just dominate.

Personally I think they might be ok when traction between sides is like 75/25. But when off roading it very common to have traction situations of 90/10 or worse. I think it’s just too much braking and it the overall system fails to work like it should.

Anyway thats my theory.

 

[AcesandEights]

Using TFL as an example (your example), they also have their roller test that proves these systems work.

 

[Wabujitsu]

Another problem I see in video after video is folks don’t know to do what has already been mentioned - keep applying throttle, DO NOT let off the throttle, then floor it, then let off, then floor it, etc. It TOTALLY defeats BLD! I had to use the system in my Sport when I had it. It worked flawlessly, because I knew how to finesse the accelerator. Also, it doesn’t engage instantly; it takes a moment or two to engage.

 

[Wabujitsu]

Go to YouTube and search “jeep wrangler brake lock differential.” It will list a ton of videos showing how BLD is supposed to work, and there are videos that explain how it works.

 

[west tex]

My '21 JL has the factory limited slip in the rear axle. If I've taken advantage of the BLD in off road situations, I haven't been aware of it but that's not to say it hasn't helped to get me out of some tough situations. I wish the Jeep LSD was the Detroit Tru-Trac, but whatever it is works pretty well in my experience.

 

[Yawnie'sPapa]

Engage duck mode. Works for crawling up snowy mountain passes according to some.

 

[6.2Blazer]

Yes, this is also my experience.

However, I don't have an LSD and my open diffs DO NOT automatically engage BLD when wheel slippage occurs. I've found I MUST press the brake manually to get BLD engaged.

I was simply asking for "best practices" because there is a lot of confusion around the BLD.

As stated many times, you shouldn't need to do anything to get BLD. The best practice is to keep applying even and smooth throttle input and let it kick in. If you are at a stop on an obstacle and apply throttle there is likely a slight delay before it engages and starts powering the other wheel. Just make sure what you think is the system not working is simply because you are staying on the throttle longer when applying the brakes. Getting on and off the throttle essentially "resets" the system each time, and as said there can be a delay in engagement, so if you are on and off the throttle you may not be giving it enough time to engage.

In general the BLD on Jeeps isn't really anything special or different from any other traction control system that has been standard on most cars for 20 years. It's all the same basic concept in functionality, with the exception they can program the computer to be more "aggressive" or sensitive in the engagement.

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