ABLS or LSD

[Bluto]

Originally Posted by Austin

The brakes aren't working against the engine. They're working *with* the differential.


The brakes will definitely not lose. They are specifically designed to clamp, which, due to their mounting location, means they're specifically designed to stop rotation of the tire/wheel.

Do you know rotors warp when subjected to thermal stress? What do you think ABLS is going to generate?

[Quad T]

Originally Posted by ChuhBaca

Thanks for the faxed beer Quad! It was a little flat, though

ROFLMAO (rolling on the floor laughing my *** off}

That was good!

[Bluto]

Originally Posted by Austin

Lucky for you, ABLS *is* a totally different system from VDC.

Did a salesman tell you that?

Sorry, I have not been to a dealer that knows more about the truck than I do.


Both systems can modify brake pressure. So, there are brake lines, brake lines for the VDC, and brake lines for ABLS?

An ABS modulator, VDC modulator, and ABLS modulator?

In low traction, I've been thoroughly disappointed with VDC over a LSD, in front wheel drive none the less. Other than not reducing engine output, I don't see how the ABLS system is any better than VDC.

[bestatchess]

It doesn't have to modulate at precision pressures to work. All it has to do is clamp.

[bestatchess]

Originally Posted by Bluto

Do you know rotors warp when subjected to thermal stress? What do you think ABLS is going to generate?

The braking load during operation of ABLS is much, much, much, much, much, much, much (did I say much?) less than during ordinary operation of the brakes. Thermal stress of the rotors is not a significant factor for ABLS operation.

[bestatchess]

Originally Posted by Bluto

Where is the brake pressure to stop 380 ft-lbs coming from???

It starts with your leg (with built in levers), the brake pedal, which is on a lever arm giving a mechanical advantage (torque=force x radius), and then there is the master cylinder, which, with power assist, translates to hydraulic pressure in the brake lines. This activates pistons in the calipers which clamp the brake pads against the rotors. By virtue of the same Torque=forceXradius equation, the large diameter of the Titan rotors provides a further mechanical advantage.

You are not understanding that the ordinary braking torque required to stop the 5,500 lb vehicle (60 to 0 in 135 ft) is way higher than 380 ft-lbs.

[Bluto]

Originally Posted by bestatchess

It doesn't have to modulate at precision pressures to work. All it has to do is clamp.

Clamping is not enough.

It clamps a wheel with no traction, the opposite wheel begin to move, it un-clamps, power returns to the wheel with less traction. Repeat and go no where.

ABLS will need to clamp and gradually modulate pressure up and down.

If it stays clamped, you are dragging a wheel.

If it fully unclamps, you will lose traction in an instant.

[Bluto]

Originally Posted by bestatchess

The braking load during operation of ABLS is much, much, much, much, much, much, much (did I say much?) less than during ordinary operation of the brakes. Thermal stress of the rotors is not a significant factor for ABLS operation.

Braking during ordinary operation distribute force evenly over the entire rotor. ABLS will clamp one section. Fully engaging a brake on one section of the rotor and gradually stopping aren’t the same.

When you are at a stop light, do you apply all of your brake force, or just enough to hold the truck?

[Bluto]

Originally Posted by bestatchess

It starts with your leg (with built in levers), the brake pedal, which is on a lever arm giving a mechanical advantage (torque=force x radius), and then there is the master cylinder, which, with power assist, translates to hydraulic pressure in the brake lines. This activates pistons in the calipers which clamp the brake pads against the rotors. By virtue of the same Torque=forceXradius equation, the large diameter of the Titan rotors provides a further mechanical advantage.

You are not understanding that the ordinary braking torque required to stop the 5,500 lb vehicle (60 to 0 in 135 ft) is way higher than 380 ft-lbs.

I know how brakes work. I want to know where ABLS gets the pressure from.

[bestatchess]

Originally Posted by Bluto

Braking during ordinary operation distribute force evenly over the entire rotor. ABLS will clamp one section. Fully engaging a brake on one section of the rotor and gradually stopping aren’t the same.

When you are at a stop light, do you apply all of your brake force, or just enough to hold the truck?

It doesn't matter whether you are applying maximum possible clamping force or just enough to stop the wheel. Once the wheel is stopped, there is no friction between pad and rotor, and thus no thermal stress. Clamping one section of a stopped rotor won't hurt anything.

[Austin]

Originally Posted by Bluto

Do you know rotors warp when subjected to thermal stress? What do you think ABLS is going to generate?

I once went through 2 sets of front rotors and a set and a half of front Porterfield R4 pads in a single track day. I had no problem keeping up with that silly Porsche, I just had problems braking like he did...

Yes, I understand brake disc rotors are subjected to thermal stress. In addition to the discs, the pads, calipers, housings, brake fluid and wheel bearings are other components subjected to heat/thermal stress from the brake system.

Originally Posted by Bluto

Did a salesman tell you that?

Sorry, I have not been to a dealer that knows more about the truck than I do.

Salespeople generally have fairly insufficient technical knowlege for my tastes. I've called 1.800.NISSAN3 quite a few times, but they're also fairly inept in explaining the design behind the concepts. 1.800.NISSAN1 - the consumer affairs department - is actually pretty damn good about getting back to you with the specific information you ask for.

My main source of information about the Titan, however, is that handy dandy factory service manual. I've read it cover to cover... a few times...

Originally Posted by Bluto

Clamping is not enough.

It clamps a wheel with no traction, the opposite wheel begin to move, it un-clamps, power returns to the wheel with less traction. Repeat and go no where.

ABLS will need to clamp and gradually modulate pressure up and down.

If it stays clamped, you are dragging a wheel.

If it fully unclamps, you will lose traction in an instant.

ABLS doesn't just clamp or not clamp. It's not a yes or no, one or zero thing. All ABLS needs to do to get the other wheel turning (the one with traction) is apply a small amount of brake force to the spinning (low traction) wheel - just enough to allow some torque to be generated and distributed to the side with traction.

[Bluto]

Originally Posted by Austin

ABLS doesn't just clamp or not clamp. It's not a yes or no, one or zero thing. All ABLS needs to do to get the other wheel turning (the one with traction) is apply a small amount of brake force to the spinning (low traction) wheel - just enough to allow some torque to be generated and distributed to the side with traction.

My post (and use of 'clamp') was in response to bestatchess. He stated "It doesn't have to modulate at precision pressures to work. All it has to do is clamp."

How would you describe what ABLS does?

Once some "torque is generated and distributed to the side with traction", then what happens? Does ABLS stop applying brake force to the wheel? What keeps the torque there?

The braking force essentially closes the open differential, sending power to the wheel with traction. Once it stops, the differential is re-opened, and spinning will resume. Pinion gears move in both directions. Power will follow the path of least resistance. The brake force provides more resistance than the wheel with traction.

The required amount of torque transferred will not always be the same. Hence different amounts of brake force are needed. Climbing a hill or obstacle will require more torque than driving on level ground.

Think of a steep driveway, with the right-half covered in ice. You will need continuous brake force applied to the right caliper, providing enough torque to the left tire, to move the truck up the driveway.

If the driveway were flat, you would not need the same amount of torque to move the truck at the same speed.

[moose44]

Originally Posted by Bluto

Once some "torque is generated and distributed to the side with traction", then what happens? Does ABLS stop applying brake force to the wheel? What keeps the torque there?

Yes the ABLS will stop applying brake force to the wheel. However, it will reengage so fast once the wheel looses traction again that it will not be noticed. If the wheel with traction begins to slip also, I believe that the ABLS in effect becomes a variation of posi. The ABLS is trying to create "equal" torque on both wheels, so if both start to spin the torque is equal for both. Since ABLS is on both axles, this will/could happen in the front and back at the same time. I don't know to what extent torque is transfered to those wheels, but if you have the e-locker it will be full power to the rear (1/2).

[Austin]

Originally Posted by Bluto

How would you describe what ABLS does?

Here is a cut'n'paste of my response from this thread:

Originally Posted by Austin

To say it more precisely, an open differential will deliver equal amounts of torque to both sides.

This means it's important to understand torque - torque is a twisting or turning force.

For torque to be generated, there must be something to push against. If there is no resistance to turning a wheel, then very little torque is generated to turn the wheel - effectively none. With an open differential, the equal amount of torque is applied to the other wheel - effectively none.

That means that when one wheel leaves the ground or is in a zero traction situation, that wheel requires effectively zero torque to turn it. An open differential delivers exactly that amount of torque - effectively none - and it delivers that amount of torque to both sides.

Remember, to generate torque, there must be some resistance to turning or twisting.

Active Brake Limited Slip simply gives the open differential something to push against. When one wheel leaves the ground or is in a zero traction situation and begins to spin, ABLS will act to apply brake force to that wheel and that wheel only. To the open differential, this has the same effect as having traction with that wheel - there is now something to push against, allowing torque to be produced and delivered equally to both wheels.

Most reports of ABLS I've read indicate it works as designed. If, in fact, it *does* work as designed, it's the neatest thing since sliced bread. The driveability and low maintenance of an open differential with the traction of a limited slip differential. You get to have your cake and eat it, too.

That's how ABLS and open differentials work.



VDC is the system responsible for reducing engine output to limit wheelspin.

When you mash the gas and one rear wheel begins to spin (begins to lose traction), ABLS acts to apply brake force to that wheel - allowing the open differential to generate torque and be delivered equally to both wheels - giving torque back to the wheel with traction.

At this point, if both wheels spin and VDC is turned on, VDC will act to reduce engine output to reduce wheel spin. If VDC is turned off, you'll sit and spin both rear wheels.

And here is titanized's reply from this thread:

Originally Posted by titanized

... I do have a CC SE 4x4, and have played in the sand, on my own dirt road and on construction sites. In 2wd, on a straight line, if I stomp on the gas, because there is so much power, both rear wheels break loose leaving very deep ruts and the ABLS light never comes on. If you are positioned to make right hand turn (in 2wd), the right rear wheel spins like hell and the ABLS kicks in and the right still turns faster but the rear left will start to break loose (finally getting some of the power) and it has pulled through. Just last night, I was playing around in 2wd until I stopped, I tried to resume, and the right started to break loose, then the ABLS kicked in, and they both dug holes (not moving) turn the dial to 4wd(hi) and she pulled right out. I think the ABLS works great, and has engaged when it is needed...

[kmfernandez]

Originally Posted by Bluto

How would you describe what ABLS does?

or doesn't do as the case may be. BigHawaii wrote this earlier in this thread:

Originally Posted by bighawaii

sorry if i was to blunt and general. in my driving experiences ive concluded that the ABLS isnt programmed to completely stop all wheel spin on all 4 tires under heavy loads rendering you a sitting duck. im sure theres other drivers out there who turned off thier VDC and had 1 or more tires spinning. at certain times when the ABLS kicks in depending how hard you feed it and the surface you are on it may slow the spinning wheel or wheels down causing the other/others to grab traction propelling you foward, on unstable surfaces it may apply braking to hard or suddenly causing both wheels to spin . i cant be the only one getting my titan dirty.

...and over in the tech. discussion thread 'Brake Active Limited Slip' he wrote:

Originally Posted by bighawaii

i dont think you want VDC to be full time since the VDC cuts your engine power rendering you helpless when both tires are slipping, if you turn it off with the VDC switch you can bring your engine up to any rpm you want, even with ABLS on. ive done it myself many times on minor trails, abls isnt "powerful" enough to stop your engine if you really juice it. when on minor trails ive found out that you have to feed it a bit and the abls will wither kick in or after a certain point wont do a thing, 1 wheel may spin or both.

It seems a little odd that so few people are reporting real-life experience...?