4x4 not working!

[jeepoch]

@mwilk012,

Respectfully, the FAD disconnects just one wheel (not both). The other is still connected to the differential. If the differential is being powered, potentially so is that one wheel.

The FAD is not intended to explicitly disable 4WD, but to lower drive train drag in 2WD hence improve overall mileage.

Notice where it's located. Along just one side of the axle. That's the wheel that no longer is attached to the differential when disconnected.

On a sophisticated (part-time or AWD) transfer case, a FAD fault can prevent the engagement of the front drive shaft but not on a purely manual one. When in full-time 4WD, the front drive shaft is powered independent of wether the FAD is connected or not.

If the ABS system does prevent BLD on a FAD failure then and only then am I wet behind the ears. Without BLD, then very little torque would be applied to the only connected wheel. Recall on a purely open diff, the wheel with the least resistance gets the vast majority of torque. However, I'm pretty sure that the speed sensors on each wheel are the only input to the ABS. But I confess I'm not 100% certain.

I'm not stubborn, just a stickler for detail. Please, prove me wrong.

Jay

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[mwilk012]

@mwilk012,

Respectfully, the FAD disconnects just one wheel (not both). The other is still connected to the differential. If the differential is being powered, potentially so is that one wheel.

The FAD is not intended to explicitly disable 4WD, but to lower drive train drag in 2WD hence improve overall mileage.

Notice where it's located. Along just one side of the axle. That's the wheel that no longer is attached to the differential when disconnected.

On a sophisticated (part-time or AWD) transfer case, a FAD fault can prevent the engagement of the front drive shaft but not on a purely manual one. When in full-time 4WD, the front drive shaft is powered independent of wether the FAD is connected or not.

If the ABS system does prevent BLD on a FAD failure then and only then am I wet behind the ears. Without BLD, then very little torque would be applied to the only connected wheel. Recall on a purely open diff, the wheel with the least resistance gets the vast majority of torque. However, I'm pretty sure that the speed sensors on each wheel are the only input to the ABS. But I confess I'm not 100% certain.

I'm not stubborn, just a stickler for detail. Please, prove me wrong.

Jay

Jay, think about it. With the front axle disconnected, the lowest point of drag is on the inner axle shaft that spins freely and neither front wheel receives any power. BLD does no function because neither front wheel spins faster than any other.

 

[jeepoch]

Jay, think about it. With the front axle disconnected, the lowest point of drag is on the inner axle shaft that spins freely and neither front wheel receives any power. BLD does no function because neither front wheel spins faster than any other.

Again not entirely true. The wheel speed sensors are connected to the wheels, not at the splines of the differential. BLD can still be applied but only when the connected wheel slips (spins faster) than the disconnected one. Since any braking action would be applied to only the slipping wheel, due to the nature of open diffs, more torque would then be applied to the disconnected spline. Delivering not much of anything in the way of tractive effort.

However, at the point that BLD reduces slip and the wheels start rotating again at the same speed, some torque will again be applied to the connected wheel. Some is better than none!

In the big picture with a disconnected FAD, the front axle will only ever be fractionally effective, depending on the traction conditions. But still, nowhere as bad as it would be with purely open diffs without BLD. This is precisely my point.

I do concede that you are effectively marginalizing my argument pretty nicely, but BLD is still nonetheless attempting to make a bad situation better. We are only quibbling over it's overall effectiveness.

I guess it's just a matter of subjective analysis. I would (of course) agree with you that attempting to off-road with a dysfunctional FAD will never be in your best interest. NEVER.

I'm just trying my best (but obviously not very well) to describe that the JL will do whatever it can to still try and help.

I wish you would have shared your first name, just to make this a little more personal. I have really enjoyed our banter. You have all my respect at criticizing my perspective throughout, and never getting derogatory.

Sincerely best regards.
Jay

 

[No Spark V6]

Again not entirely true. The wheel speed sensors are connected to the wheels, not at the splines of the differential. BLD can still be applied but only when the connected wheel slips (spins faster) than the disconnected one. Since any braking action would be applied to only the slipping wheel, due to the nature of open diffs, more torque would then be applied to the disconnected spline. Delivering not much of anything in the way of tractive effort.

However, at the point that BLD reduces slip and the wheels start rotating again at the same speed, some torque will again be applied to the connected wheel. Some is better than none!

In the big picture with a disconnected FAD, the front axle will only ever be fractionally effective, depending on the traction conditions. But still, nowhere as bad as it would be with purely open diffs without BLD. This is precisely my point.

I do concede that you are effectively marginalizing my argument pretty nicely, but BLD is still nonetheless attempting to make a bad situation better. We are only quibbling over it's overall effectiveness.

I guess it's just a matter of subjective analysis. I would (of course) agree with you that attempting to off-road with a dysfunctional FAD will never be in your best interest. NEVER.

I'm just trying my best (but obviously not very well) to describe that the JL will do whatever it can to still try and help.

I wish you would have shared your first name, just to make this a little more personal. I have really enjoyed our banter. You have all my respect at criticizing my perspective throughout, and never getting derogatory.

Sincerely best regards.
Jay

You're right that BLD only cares about difference in wheel speed but I think the point that @mwilk012 is making is that the wheels never get the ability to slip because the FAD is disconnected and the inner shaft will just continue to spin. The passenger front tire is disconnected due to the FAD being disengaged and the driver tire won't propel you forward since the open diff is going to allow the inner shaft to spin. As far as BLD is concerned both front wheels aren't moving so its not going to intervene.

 

[mwilk012]

Again not entirely true. The wheel speed sensors are connected to the wheels, not at the splines of the differential. BLD can still be applied but only when the connected wheel slips (spins faster) than the disconnected one. Since any braking action would be applied to only the slipping wheel, due to the nature of open diffs, more torque would then be applied to the disconnected spline. Delivering not much of anything in the way of tractive effort.

However, at the point that BLD reduces slip and the wheels start rotating again at the same speed, some torque will again be applied to the connected wheel. Some is better than none!

In the big picture with a disconnected FAD, the front axle will only ever be fractionally effective, depending on the traction conditions. But still, nowhere as bad as it would be with purely open diffs without BLD. This is precisely my point.

I do concede that you are effectively marginalizing my argument pretty nicely, but BLD is still nonetheless attempting to make a bad situation better. We are only quibbling over it's overall effectiveness.

I guess it's just a matter of subjective analysis. I would (of course) agree with you that attempting to off-road with a dysfunctional FAD will never be in your best interest. NEVER.

I'm just trying my best (but obviously not very well) to describe that the JL will do whatever it can to still try and help.

I wish you would have shared your first name, just to make this a little more personal. I have really enjoyed our banter. You have all my respect at criticizing my perspective throughout, and never getting derogatory.

Sincerely best regards.
Jay

My name is Matt.

The problem with BLD combined with FAD operation is that the front wheeis will never turn faster than desired , as you said yourself, the speed sensors are at the wheel end. The front wheels will turn only as fast as the vehicle is being moved by the rear tires that are powered normally.

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