Great explanation. I put Truetracs front and back in my jeep. Will the BLD compliment the truetrac operation if one wheel is off the ground?
Great question! The truetrac, and any limited slip differential (LSD), will actually kick in prior to the BLD system. This means that if a wheel looses traction the LSD will trigger first and if it is enough to overcome the obstacle then the BLD will not be needed. However if the LSD is not enough to overcome, then the BLD will go into affect.Great explanation. I put Truetracs front and back in my jeep. Will the BLD compliment the truetrac operation if one wheel is off the ground?
I believe that the situation you describe above is correct. An LSD can shift it back to ~3:1 towards one wheel. The BLD should further perpetuate it so long as the spinning wheel has ground contact.Green machine, Great job with that. I do have one question about your explanation. My understanding of and experience with open diffs (principally on Porsches) includes a subtle difference from your explanation. When one wheel has zero traction it receives 100% of the motor's torque. In other words, all torque is still made by the motor, and that torque seeks the path of least resistance; if one wheel (speaking of a 2WD axle now) has less traction than the other but still some traction the torque will go in inverse proportion to the low-traction axle. So that if that wheel has zero traction, 100% of the torque will go to that wheel. To see this in action, get your open diff Jeep or car stuck in snow. Then put a traction block of some sort under one wheel, giving it adequate traction to back the car up. When you apply torque to the rear axle, one wheel stays perfectly stationary, and one spins furiously. This works in a manual gearbox as well as auto, and there is no torque converter in the manual to absorb a small amount of torque (such as when you sit at a light with an automatic, the engine is turning but the car is not moving; the torque at idle is being absorbed by the torque converter. But a manual doesn't do that; it would stall the motor if even a tiny amount of torque goes through the gearbox but is unable to spin a wheel.) So what I'm saying is, the "small amount of torque, let's say 15 ft/lbs" that in your example was making its way to the wheel with traction, couldn't be doing that in a manual Jeep -- that 15 ft. pounds has to spin something, there's no slop in the system to absorb it. So if it were going to the wheel with traction, and that wheel weren't spinning, the motor would stall. Another way of looking at it is this: the motor will make whatever its rated torque at a certain RPM is. It cannot make less torque just because a spinning wheel doesn't require much torque. So let's that in trying to unstick it you run the motor up to 3000 rpm, and it makes 240 lbs-ft at that point. I has to send that torque out through the gearbox to the diff, and in so doing, to the wheels. The open differential chooses to send 100% (240 lbs-ft.) all to the spinning wheel, since that is the path of least resistance. But with BLD, the fact that you begin "adding traction" to the spinning wheel (at least in the "mind" of the open differential) means that it begins handing some torque back to the wheel with traction, since it's suddenly equally hard to spin the spinning wheel. And so it goes back to 50/50, as long as the BLD is willing to apply brakes hard enough to even it back up. It still may not get you unstuck, of course, if the wheel that used to have traction finds that it doesn't really have enough traction to handle the 120 lbs-ft of torque it's now getting, and starts spinning also. When that happens, whether you have open diff, LSD, or lockers you're SOL, cuz none of them manufacture traction.![]()
This is the main reason I got a Willys with LSD instead of a Rubicon, which is what I had assumed I would get when I started shopping. When I learned that the Rubicon is reduced to open diff status unless you have lockers engaged, I realized I would have far more situations where an LSD would save my bacon than situations where I needed E-lockers.The place where a locker will let you down is in situations that have intermittent slippery surfaces. As the surface goes from wet to dry, you have poor steering ability.
I did the same. I don't live in rock crawler land (though I enjoy it when I get the chance). The LSD is exceptionally capable. I've been in a couple of places where a locker would have made things easier, but I've yet to find something I couldn't do w/o them.This is the main reason I got a Willys with LSD instead of a Rubicon, which is what I had assumed I would get when I started shopping. When I learned that the Rubicon is reduced to open diff status unless you have lockers engaged, I realized I would have far more situations where an LSD would save my bacon than situations where I needed E-lockers. (plus, for my world, I've found the 4:1 and 4.10 combination just too dang low for me. 2.72:1 and 3.73 works perfect around my part of the world. Well, plus the Willys is just so dang cool looking.)
Yes we do. The BLD feature significantly improves the Rubicon handling in wet/slippery/snow/icy conditions. It offers a whole new dimension to what conditions all JK's can handle. Many of these recent posts about the Subaru and other AWD vehicles outperforming the Jeep are not only amusing, but make me wonder why BLD isn't mentioned more in these "exchanges."I did the same. I don't live in rock crawler land (though I enjoy it when I get the chance). The LSD is exceptionally capable. I've been in a couple of places where a locker would have made things easier, but I've yet to find something I couldn't do w/o them.
To be fair to the Rubicon folk, they do in fact have BLD, so it's not a totally open diff.
I believe you misunderstood me, GreenMachine. I am saying that it does only require a small amount of torque (not zero) to spin a tractionless wheel, but the ENGINE has to make whatever it makes -- say 240 lb-ft. So that torque HAS to go somewhere. Other than the amount that is consumed at all times by driveline losses (say 40 lb-ft) the rest HAS to go to the wheel or wheels. In a manual, ZERO torque can go to a stationary wheel, or you will stall the engine. But with an open diff, ZERO torque does go to the wheel with traction, and 100% of the torque gets sent to the spinning wheel.NoGaBiker. The freely spinning wheel will will not require zero torque to spin because it still have some weight to the actual wheel and probably some resistance if it's just on snow or mud.
So where does the remaining 210 lb-foot of torque go, if only 30 of it is going to the two wheels in your illustration? You see my point? It ALL goes to the spinning wheel, and none of it goes to the wheel with traction.The engine produces it's max torque and you can hear it as the RPMs skyrocket but the spinning wheel will only required 15 ft-lbs of that available torque to get it moving and therefore the other wheel can only get the same amount.
The results are as you say, but not for those reasons. The spinning wheel is getting 100% of torque because the torque wants to go the path of least resistance in an open diff. Now you begin applying the brake to that wheel only, by means of the BLD, which tricks the diff into thinking you've gotten traction over there. So it begrudgingly begins to send less torque to the spinning wheel, and more to the wheel with traction until one of two things happens:The BLD applies the brake to the spinning wheel causing it to need to use more of the available torque to spin it. It keeps applying the brake until the other wheel with traction is able to spin at the same speed. Essentially it's allowing the jeep to use the available torque that it's making.
[/QUOTE]I believe you misunderstood me, GreenMachine. I am saying that it does only require a small amount of torque (not zero) to spin a tractionless wheel, but the ENGINE has to make whatever it makes -- say 240 lb-ft. So that torque HAS to go somewhere. Other than the amount that is consumed at all times by driveline losses (say 40 lb-ft) the rest HAS to go to the wheel or wheels. In a manual, ZERO torque can go to a stationary wheel, or you will stall the engine. But with an open diff, ZERO torque does go to the wheel with traction, and 100% of the torque gets sent to the spinning wheel. So where does the remaining 210 lb-foot of torque go, if only 30 of it is going to the two wheels in your illustration? You see my point? It ALL goes to the spinning wheel, and none of it goes to the wheel with traction. The results are as you say, but not for those reasons. The spinning wheel is getting 100% of torque because the torque wants to go the path of least resistance in an open diff. Now you begin applying the brake, which tricks the diff into thinking you've gotten traction over there. So it begrudgingly begins to send less torque to the spinning wheel, and more to the stuck wheel until one of two things happens: 1) the increased amount of torque going to the wheel with traction overcomes that traction before the Jeep has enough traction to move, and now you have two wheels spinning with equal amounts of torque being sent to them. Or 2) the increased amount of torque is sufficient to move the Jeep on that one wheel that has traction, until the other wheel regains traction and all is well. But the takeaway here is that all of your torque (as determined by throttle position and engine rpms) WILL go to your two driven wheels -- nowhere else for it to go. The ratio will be determined by the diff. Cheers!
I read several articles while doing my research. I think my description is fairly on par.The spinning wheel is getting 100% of the available torque whether it needs it or not. Period. Engine revs do not shoot up when you spin a wheel unless you push the throttle further.
Yes, that's exactly what us "old guys in old 4wds used to do by applying a little bit of E-brake."Man, what a cool thread and a cool idea from Jeep. So in turn, the BLD does what old guys in old 4wds used to do by applying a little bit of E-brake. COOL!!!!
Thanks for the clarification, and to stop me from perpetuating bad info on the net!NoGaBiker. The freely spinning wheel will will not require zero torque to spin because it still have some weight to the actual wheel and probably some resistance if it's just on snow or mud. The engine produces it's max torque and you can hear it as the RPMs skyrocket but the spinning wheel will only required 15 ft-lbs of that available torque to get it moving and therefore the other wheel can only get the same amount. The BLD applies the brake to the spinning wheel causing it to need to use more of the available torque to spin it. It keeps applying the brake until the other wheel with traction is able to spin at the same speed. Essentially it's allowing the jeep to use the available torque that it's making. Cornfed. The BLD is actually designed to overcome obstacles where one tire or more tires are in the air.