OK, I wasn't sure where to put this info so I will put it here as a write up. Here is a speech I have given many many times and Maverick loves to hear it.


ESP tries to correct for you using the brakes to keep you pointed in the right direction and not turn over. The traction control system doesn't want your wheels to spin, so it cuts power, applies brakes to keep that from happening. BLD, (brake lock differential,) doesn't care if the wheels are spinning, just as long as they are spinning at the same rate.
Now, in 2wd, or 4hi, both esp and traction control are on all the time. In either of these modes pressing the esp button once will turn off traction control only. You will get a little amber light of a car with squigly lines coming behind the tire. This only disables the part of esp that doesn't want you to spin the tires, but it will still try to keep you on course and from rolling over.
In 4hi, if you step on the clutch or slip it in neutral and hold the esp for several seconds, it will disengage esp and traction control. This means no electronic nannies, just like an old jeep. You will have the amber traction control light on, and also a message in your info center that says ESP off. (We will talk about BLD in just a second.)
In 4lo, there is only one setting, everything off, like the above paragraph, but it does it automatically, and cannot have either traction control or esp turned on.

...BLD's are not as good as lockers! However they greatly expand the capability of jeeps that were not ordered with lockers. IMO, they are better than a plain lsd, although on a wrangler with lsd and bld, it enhances both systems. Now for how they work.

All jeep jk's have an open differential unless the lsd is ordered in which case the rear diff only has the limited slip differential installed, I include jeeps with lockers here since when the lockers are disengaged they function as an open rear end.
In an open diff, both wheels get the same amount of torque from the motor at all times. The problem of this is easily demonstrated in a worse case scenario where one wheel is in the air, and the other is on solid pavement. You would think that since one wheel was on good footing it can pull the jeep right? Wrong. What will happen is that when you give it gas, the wheel in the air will spin and the one on solid ground will do nothing! This is because it may only take 10ft. lb. of torque to turn the wheel in the air since there is no resistance. Both wheels will get 10 lb. of torque, but 10 lbs of torque is not enough to move the wheel with the resistance (solid traction,) so it does not move.

Here is where BLD comes into play. It will apply the brake to the wheel in the air, increasing the amount of torque needed to overcome the resistance. When the torque is high enough, it can and will move the wheel on the ground, both wheels are still getting the same amount of torque, but the brake is creating a need for more torque to turn the wheel in the air, which means the one on the ground gets enough torque to turn it.

Lockers in the JK function just like the described above, until the lockers are engaged. when they do there is a mechanical link between both wheels so that they are physically unable to turn any faster or slower than the other wheel. This is the maximum traction set up.
Back to our example if one wheel is in the air and one on the ground, no problem, if the air wheel spins, so does the one on the ground. This is the best set up for offroad situations, but locked diffs when engaged reduce your turning capabilities and should not be used on pavement.

BLD equipped jeeps can go through many things that the ones with true lockers can, but it is sometimes jerkier, not as smooth, and you have to apply more power, (gas) to overcome the force of the brakes clamping down on the spinning wheel. Lockers are the way to go for ultimate traction, and control.

Next up LSD....I think lsd is the hardest to explain, but to keep it simple, it can by itself without the use of BLD transfer up to 2.7x the amount of torque across the wheels. This means if one wheel has slightly less traction and only needs 20 lbs torque to spin, the lsd can send almost 60 lb. of torque to the other wheel. There is nothing wrong with driving an lsd on the road, it is always active and is better than an open diff for offroad, but not as good as a locker. Why?
Well back to the original example one wheel in the air with zero traction. 10 lb of torque x 2.7 equals about 30 lb of torque, probably not enough to move the wheel.
So if you had a choice, I should think that BLD is a better offroad system than lsd, but jeep one ups me, because the bld is on the lsd too(omg all the acronyms.) It functions the same way, but does not have to intervene as much, and in situations such as dirt or sand where the torque bias is not as high as one wheel in the air, the lsd can transfer torque quicker and smoother across the wheels, but the bld's are stil there to step in if the torque bias is higher than the lsd can overcome and neither the bld or the lsd have to work as hard as they would were it only one or the other. This is a pretty sweet setup.

One more thing, When you're lockers are engaged, there is no need for bld since there is no way for there to be a speed difference across the axle.
BLD is on both the front and rear differentials.

That is the short of it, I know a few more things if you need to know, as well as have plenty of first hand knowledge of these systems.

wow Ben- did you actually write all that?

Nice job!

Here's an example of BLD at work on the front. Watch the drivers side tire- it will spin for a second and then the BLD kicks in giving power to the passenger side (which has traction), and pulls me up




The big key to BLD (and the part that has to be learned for it to be effective) is that the instant you notice a wheel spinning, stay on the throttle but don't hit the throttle harder. Most people react one of two ways when a wheel starts to spin: they either let off the throttle completely, or they slam on the throttle . Both of those are the wrong things to do. Letting off the throttle does nothing (of course). Slamming on the throttle just makes it more difficult for the BLD to brake the spinning wheel, and virtually guarantees that when the BLD does kick in, it will have way too much power- so you'll either break traction with the wheel you're trying to get power too, or you'll have a big lurch forward when the traction side grabs... The key to effective use of the BLD is (when you feel the wheel spin) just stay on the throttle and wait for the BLD to kick in. Once it has kicked in, it may or may not have enough power to pull you. Its at that point that you can actually apply some more throttle- ease into it, don't slam it. Just ease into the throttle until it has just the right amount of torque for the tire to pull you up.

This type of driving does not come naturally. It is something you learn and have to get used to. I got really good at using my BLD. So much so that I debated even bothering with lockers- my BLD's were getting me thru everything effectively enough (I thought). But now I love the lockers. So much easier.

i don't have time to look, but there is a vid out there of a jk with a front wheel in the air and the other on the ground the bld works awesome

I think Maverick has some vids of my bld's working. N2, yes I did write all that. I love mechanical processes and things. Physics has always fascinated me, especially force/leverage/potential/kinetic energy etc. And good addendum to the driving style variation! Here is a link to a vid of my jeep trying to get up a sand hill and some of the commentary that made me want to post the above. (BTW, I wrote that a while back and saved it to my comp so now I can just copy/pasta my epic BLD speech.) Maverick hates it.

http://www.youtube.com/watch?v=_MSGsQpVmnU

Great write up Ben. Thanks for all that info. It answered a lot of questions but got me confused a little, mainly between "traction control" and BLD. From your description, both seem to brake the spinning tire. Is BLD always on, or only in 4Lo or 4Hi /w traction control off? I guess that is where I got confused. I have LSD and no lockers in case that matters.

Was your video in 4Lo or 4Hi? And what a cliff hanger! Is your jeep still there or did she ever get out?

Go Captain Planet. "By your powers combined!"

Between those two post I now completely understand. Thank you so much.

Ben wrote:

And sadly, I did not make it up that sand hill.

well at least you two don't discriminate- you'll fug up any thread, including your own

I have Eaton E-Lockers front and rear. Should I install BLDs?

And Ben, the ratio spacing on the 6-speed is probably due mostly to the very low (numerically) gear ratio with the tall tires. You move up to, say, 4.56 or 4.88, and you might be annoyed that you don't have a taller 6th gear cruising ratio.

Probably and yes good sir, you should retrofit BLD's. Everyone needs them! In all seriousness what I do like about them is that they give the jeeps that aren't optioned with lockers a lot more capability without adding so much to the cost of the vehicle. In fact i would postulate that it is cheaper for jeep to put bld systems in than it was to put the lsd's in previous gen jeeps.

Ok, I understand. Thanks for the info.





Teacher may I go to the restroom, I need to pee :jk:

BLDS R SRS BUSINESS!!!!

You spam fags stay teh fuck outta my BLD THREAD!