Jeep Garage  - Jeep Forum banner

21 - 40 of 48 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter #22
Thanks to all for the replies, I am getting close to pulling the trigger.

So am I correct when I believe that I am unable to own a Grand Cherokee Limited with the QDII? I see I am able to find them with the QTII. Is their that big of a difference, I know the QDII will allow me to lock the rear differential or something like that. What do I have to do to get the QDII?

Thanks! :)
 

·
Super Moderator
Joined
·
8,499 Posts
The Only way to get QD-II on a Limited is with the Off-Road Adventure Pack II for MY20


It's also important for you to know that the ELSD that comes with QD-II isn't something you generally get to turn off an on. It's more or less an automatic feature. It's not a "hard locker" like on wheeling machines of the past.
 

·
Registered
Joined
·
1,251 Posts
The Only way to get QD-II on a Limited is with the Off-Road Adventure Pack II for MY20


It's also important for you to know that the ELSD that comes with QD-II isn't something you generally get to turn off an on. It's more or less an automatic feature. It's not a "hard locker" like on wheeling machines of the past.
My impression is that the eLSD is unconditionally enabled when in 4WDLow along with the front differential.
Jim, is that right or wrong?
 

·
Registered
Grand Cherokee
Joined
·
3,243 Posts
Pretty sure shifting into 4WD Low applies maximum pressure to the clutchpack in the transfer case and rear differential, to lock it.....
In Automatic 4WD, the default mode, the clutch packs are controlled by the 4WD module and vary clutch pressure according to the conditions... ...the transfer case won't lock in the Automatic 4WD mode, but the ELSD in the rear Diff can lock in Automatic 4WD if needed...
 

·
Super Moderator
Joined
·
8,499 Posts
My impression is that the eLSD is unconditionally enabled when in 4WDLow along with the front differential.
Jim, is that right or wrong?
Most likely...but my answer was more that the vehicle is what determines if it's active or not unlike in the past when one could flip a lever or push a button or crawl on the ground and turn the hubs to lock things up. I've never looked into the specifics and honestly, only ever used 4-low maybe three times in the 7 years I owned my JGC ; once to test and twice when using a tow strap to pull another vehicle out of trouble.
 

·
Registered
Joined
·
1,251 Posts
Pretty sure shifting into 4WD Low applies maximum pressure to the clutchpack in the transfer case and rear differential, to lock it.....
In Automatic 4WD, the default mode, the clutch packs are controlled by the 4WD module and vary clutch pressure according to the conditions... ...the transfer case won't lock in the Automatic 4WD mode, but the ELSD in the rear Diff can lock in Automatic 4WD if needed...
I always assumed in 4Low the eLSD is not acting as a true LSD but acting as a rear differential locker.
The eLSD clutches in 4Low as you mention are engaged 100% of the time to emulate a locker.
This all makes sense because of this excerpt in the Owner's Manual:

"When additional traction is required, the 4WD LOW
position can be used to lock the front and rear driveshafts
together and force the front and rear wheels to rotate at the

same speed. The 4WD LOW position is intended for loose,
slippery road surfaces only
. Driving in the 4WD LOW

position on dry, hard-surfaced roads may cause increased
tire wear and damage to driveline components."
 

·
Registered
Joined
·
24 Posts
I always assumed in 4Low the eLSD is not acting as a true LSD but acting as a rear differential locker.
The eLSD clutches in 4Low as you mention are engaged 100% of the time to emulate a locker.
This all makes sense because of this excerpt in the Owner's Manual:

"When additional traction is required, the 4WD LOW
position can be used to lock the front and rear driveshafts
together and force the front and rear wheels to rotate at the

same speed. The 4WD LOW position is intended for loose,
slippery road surfaces only
. Driving in the 4WD LOW

position on dry, hard-surfaced roads may cause increased
tire wear and damage to driveline components."
I believe that quote refers to the transfer case, not the rear differential?
 

·
Registered
Joined
·
1,251 Posts
I believe that quote refers to the transfer case, not the rear differential?
Yeah i realize the front diff is locked with the rear diff in 4Low via the Tcase but depending on how the eLSD clutch system works in the rear diff, i could see how the rear diff could also be implemented as a locker in 4Low.
That might be wishful thinking. Only way short of published FCA specs. is to test and see what happens.
 

·
Registered
Grand Cherokee
Joined
·
3,243 Posts
Yeah i realize the front diff is locked with the rear diff in 4Low via the Tcase but depending on how the eLSD clutch system works in the rear diff, i could see how the rear diff could also be implemented as a locker in 4Low.
That might be wishful thinking. Only way short of published FCA specs. is to test and see what happens.
There is no dog clutches in the system, when we say locked, it means the clutch pack has full force applied to it and will not slip...... ....which is the same as locking it....

A better way to say it, the transfer case locks the rotation of the front/rear driveshaft to the same speed..... ....the front differential can not lock in any of the drivetrain systems, and only QDII can lock the rear differential.....

For QTII and QDII, the rear driveshaft is directly driven, the front driveshaft has the clutchpack between it and the rear driveshaft.... ..so only the front driveshaft can have less than or equal torque than the rear, but never more and then only less torque while the clutch pack is slipping...

Automatic 4WD mode of the MP3023 Transfer case, used in QTII and QDII, the clutch pack is engaged at partial pressures that it changes according to conditions. This transfer case does have a RWD mode, it's used in trucks, but the WK2 doesn't use the mode, the SelectTerrain knob will vary the pressure the clutch for different "pre-loads" or torque bias, something I think only Jeep does....

The eLSD, I could be wrong, but I've seen plenty of info, including someone monitoring its operation with AlfaOBD, that it works like a regular LSD, with the 4WD module varying the "pre-load" or pressure on the clutch pack according to conditions, and goes to full pressure as conditions dictate, and goes to full pressure when you shift into 4WD LOW.... ....the poster about monitoring with AlfaOBD commented how surprised he was about how often the eLSD was locking up during normal driving....

Pre-Load is a term for the old LSD's, there were springs in the purely mechanical LSD's, that put pressure on the clutch pack... ...folks would swap out the springs to tighten or loosen the clutch pack, called the pre-load.... ...it's the same things as Torque Bias.... ....how much pressure on the clutch pack determines how much torque difference is needed to get it to slip, and then it how much of a torque split results while it slips... ...if the clutch pack is not slipping then both driveshafts on either side of the clutch pack are turning at the same speed and thus have the same torque and power.... ...if the clutch pack is slipping then drive shafts are turning at different speeds, and thus different power, thus different torque.....
 

·
Registered
Joined
·
1,251 Posts
There is no dog clutches in the system, when we say locked, it means the clutch pack has full force applied to it and will not slip...... ....which is the same as locking it....

A better way to say it, the transfer case locks the rotation of the front/rear driveshaft to the same speed..... ....the front differential can not lock in any of the drivetrain systems, and only QDII can lock the rear differential.....

For QTII and QDII, the rear driveshaft is directly driven, the front driveshaft has the clutchpack between it and the rear driveshaft.... ..so only the front driveshaft can have less than or equal torque than the rear, but never more and then only less torque while the clutch pack is slipping...

Automatic 4WD mode of the MP3023 Transfer case, used in QTII and QDII, the clutch pack is engaged at partial pressures that it changes according to conditions. This transfer case does have a RWD mode, it's used in trucks, but the WK2 doesn't use the mode, the SelectTerrain knob will vary the pressure the clutch for different "pre-loads" or torque bias, something I think only Jeep does....

The eLSD, I could be wrong, but I've seen plenty of info, including someone monitoring its operation with AlfaOBD, that it works like a regular LSD, with the 4WD module varying the "pre-load" or pressure on the clutch pack according to conditions, and goes to full pressure as conditions dictate, and goes to full pressure when you shift into 4WD LOW.... ....the poster about monitoring with AlfaOBD commented how surprised he was about how often the eLSD was locking up during normal driving....

Pre-Load is a term for the old LSD's, there were springs in the purely mechanical LSD's, that put pressure on the clutch pack... ...folks would swap out the springs to tighten or loosen the clutch pack, called the pre-load.... ...it's the same things as Torque Bias.... ....how much pressure on the clutch pack determines how much torque difference is needed to get it to slip, and then it how much of a torque split results while it slips... ...if the clutch pack is not slipping then both driveshafts on either side of the clutch pack are turning at the same speed and thus have the same torque and power.... ...if the clutch pack is slipping then drive shafts are turning at different speeds, and thus different power, thus different torque.....
Mongo i fully realize when in 4Low that the front and rear diffs are ridgedly locked together via the Tcase clutching system...the reason the warning not to drive on dry pavement while in 4Low.
What is puzzling is that FCA does not publish specific details on how the rear diff's eLSD functions in 4Low at least that i could find.
I could easily see how they could of designed the rear eLSD diff system to act as a locker only in 4Low.
Whether thats the case, no idea but i doubt it. After all WK2's are not Wranglers.

Far as the old school Mopar mechanical rear diff LSD clutch systems go, all one has to do for 100% dedicated off roading use is not to add or reduce the friction modifier additive to the rear diff fluid which tends to keep the clutch from slipping.
Bingo!.. more or less a rear diff locker.
 

·
Registered
Grand Cherokee
Joined
·
3,243 Posts
Mongo i fully realize when in 4Low that the front and rear diffs are ridgedly locked together via the Tcase clutching system...the reason the warning not to drive on dry pavement while in 4Low.
I know what you mean. But what your saying can confuse people.....
The front differential is an open differential and so is the rear for all but the QDII equipped WK2's... ...they can not lock.... ....the pinion gears of the differentials are locked together at best....
Arguably, locking a driveshaft with a clutch, that the clutch won't slip at the torque the shaft would usual experience, is not "rigidly" locking it.... ...a dog clutch would be needed to rigidly lock it.. .
Yes, it may sound like I'm nitpicking at minor details, but there are folks on this forum that would read that and assume shifting into 4 low would lock both front and rear differentials in the WK2.... ....which is not true at all....

What is puzzling is that FCA does not publish specific details on how the rear diff's eLSD functions in 4Low at least that i could find.
I could easily see how they could of designed the rear eLSD diff system to act as a locker only in 4Low.
Whether thats the case, no idea but i doubt it. After all WK2's are not Wranglers.
I've complained about this ad-nauseam, no one explains how their products work anymore.....
If the owner doesn't want to read it, doesn't care, then they don't have to read it, but plenty people are curious and want to know, but they can't find the info anywhere....
Used to be the Manufacturers couldn't brag enough about their technology and how everything works.... ...today its some dumbed down overview that explains nothing, if it's anything at all........

Best I can figure, liability and sales, they push any info through lawyers and marketing, and they pull out anything that can be a problem and you end up with nothing but empty words describing nothing....
Maybe its revenge, can you blame them, all the regulators are constantly telling the manufacturers that owners/drivers can't be held responsible for their own actions, they are all babbling idiots and the manufacturer has build the cars that are smarter than them to protect them.... ....so if the owners/drivers are that stupid, how can they even possibly understand anything about how the vehicle works...

Far as the old school Mopar mechanical rear diff LSD clutch systems go, all one has to do for 100% dedicated off roading use is not to add or reduce the friction modifier additive to the rear diff fluid which tends to keep the clutch from slipping.
Bingo!.. more or less a rear diff locker.
The eLSD in the WK/XK (previous Gen) had a lot of complaints about tire scrubbing in slow tight turns, fresh fluid and friction modifier would fix it.... ...so yes, I understand what you're saying.... ...I'd still would not claim that changing diff fluid in an LSD and leaving out the friction modifier as turning it into a locker, yes it would even more limit the slip, but it won't lock it....

And that is the advantage of the eLSD, driving on road, in wet weather, its not breaking traction, doing tire scrubbing etc, when you need an LSD, its an LSD, when you need a locker, its locking.... You get the best of all three, not one that is good in one situation and bad in the others.
 

·
Registered
Joined
·
1,251 Posts
I was more or less discussing 4Low and rear diff. operation.
Yes in normal 4Hi there is a clutch system that applies torque to the front diff when wheel slippage is detected.
However if that clutch has theoretical zero slippage, for all practical purposes the front and rear diff's for a lack of a better term can be said to be ridgidly coupled together. Though I doubt the clutch has zero slippage.

Back to 4Low operation.
Its not all that clear to me what my WK2 Tcase is doing when in 4Low.
From the Owner's Manual:
....When additional traction is required, the 4WD LOW
position can be used to lock the front and rear driveshafts
together and force the front and rear wheels to rotate at the
same speed....


And also from the Owner's Manual, the 4HI to 4Low shifting procedure:

With the vehicle at speeds of 0 to 3 mph (0 to 5 km/h), the
ignition switch in the ON position or the engine running,
shift the transmission into “N”, and push the “4WD LOW”
button once on the transfer case switch.......
.....NOTE: If shift conditions/interlocks are not met, or a
transfer case motor temperature protection condition exists......


This suggest to me that both differentials are mechanically locked together by a gear or dog system.
The WK2's 4Hi to 4Low shifting procedure is just about identical for both my F150 and Jeep XJ where i know for a fact both diffs are mechanically locked together.

With my F150's Tcase, when its put in 4Low an electrical motor meshes gears to ridgidly lock both diff's apparently the same with the WK2.
My XJ's Tcase on the other hand uses a hand lever instead of a motor, to mesh Tcase gears via an internal shift fork.
With both my F150 and XJ, if the shifting procedure is not followed correctly you can actually here gears grinding in those Tcases. Similar to the old clash box manual transmissions that didn't use synchros to mesh gears perfectly at any speed.

Now in addition to both diffs locked in 4Low it would be great if the rear diff emulates or approaches a mechanical locker.
There's likely electrical driven clutches in the eLSD perhaps for each rear wheel.
Why couldn't both clutches be engaged full time when in 4Low to emulate a locker.
 

·
Registered
2014 Summit 5.7 4wd 20" tires swapped to 18", added all skid plates
Joined
·
1,460 Posts
Now in addition to both diffs locked in 4Low it would be great if the rear diff emulates or approaches a mechanical locker.
There's likely electrical driven clutches in the eLSD perhaps for each rear wheel.
Why couldn't both clutches be engaged full time when in 4Low to emulate a locker.
I don't see the need for a low speed non-competition vehicle. If it was locked all the time it would create binding, esp on hard rock surfaces when turning. As long as the system can figure out when there is a genuine need to lock (or partially lock) due to slip that would take care of it. Based on how well mine handles steep uneven uphills with near zero wheelspin I have a hard time seeing the need/benefit to a just lock it up strategy. I can even see possible situations when an unnecessarily locked rear could create a sideways skid that would not otherwise occur if only partial lock was in effect.. along the lines of how in some snow conditions a locker makes things worse, not better.
 

·
Super Moderator
Joined
·
8,499 Posts
My guess is that the rear ELSD in 4Low likely works the same way it does in 4High...
 

·
Registered
Joined
·
1,251 Posts
I don't see the need for a low speed non-competition vehicle. If it was locked all the time it would create binding, esp on hard rock surfaces when turning.........
We're talking 4Low meant for serious rock crawling, pulling boats out of the water, pulling cars out of ditches or not that long ago with my XJ pulling tree stumps where the maximum engine torque and traction possible is applied to all 4 wheels binding or not.
And yes my XJ has a stock mechanical rear LSD diff.
The front diff on these vehicles is open but relies on the weight of the engine for more front wheel traction.

In all those above cases cases the occasional wheel binding that comes with 4Low is as it should be.
The reason 4Low should never be used on dry pavement at least for prolonged periods if one values their drive train.
 

·
Registered
Joined
·
1,251 Posts
My guess is that the rear ELSD in 4Low likely works the same way it does in 4High...
Jim, until i hear other wise i think you're probably right.
But still in the back of my mind, my persistent lingering question is how does the eLSD actually operate full time in 4Low?
We already know how it operates in 4Hi just like any other LSD diff.

Its so dam hard not having the official Mopar tech. manuals on just whats going on with that eLSD.
And even then, the rear eLSD diff 'might' not have any rebuild detailed diagrams but instead relies on the Jeep techs. to replace the entire diff. as a unit when defective. Don't know!
 

·
Registered
Grand Cherokee
Joined
·
3,243 Posts
I was more or less discussing 4Low and rear diff. operation.
Yes in normal 4Hi there is a clutch system that applies torque to the front diff when wheel slippage is detected.
However if that clutch has theoretical zero slippage, for all practical purposes the front and rear diff's for a lack of a better term can be said to be ridgidly coupled together. Though I doubt the clutch has zero slippage.
Actually, the clutch in the transfer case is engaged always, not just when wheel slippage is detected. The pressure varies according to conditions.

Why isn't just "Locked" good enough, why do you have say rigidily locked?

I hope, if torque was exceeded somehow on the drivetrain with the clutches at max pressure, the clutch would slip before something in the drivetrain breaks. I don't know if that is true....

If its rigidly locked, then aren't you saying it break before it slips?

Back to 4Low operation.
Its not all that clear to me what my WK2 Tcase is doing when in 4Low.
From the Owner's Manual:
....When additional traction is required, the 4WD LOW
position can be used to lock the front and rear driveshafts
together and force the front and rear wheels to rotate at the
same speed....


And also from the Owner's Manual, the 4HI to 4Low shifting procedure:

With the vehicle at speeds of 0 to 3 mph (0 to 5 km/h), the
ignition switch in the ON position or the engine running,
shift the transmission into “N”, and push the “4WD LOW”
button once on the transfer case switch.......
.....NOTE: If shift conditions/interlocks are not met, or a
transfer case motor temperature protection condition exists......


This suggest to me that both differentials are mechanically locked together by a gear or dog system.
The WK2's 4Hi to 4Low shifting procedure is just about identical for both my F150 and Jeep XJ where i know for a fact both diffs are mechanically locked together.
Nowhere in that write up do they say both differentials are locked together. Like I said before, I know what you mean, I only point it out because there are plenty of folks that will be confused by this statement, differentials are not being locked. You might note, the O.M. choose to word it like I do, it locks the front and rear driveshafts together to turn at the same speed..... .....nothing changes in the differentials, yes the input to both are turning at the same speed but the output of the differentials can turn at different speeds....

Also, nowhere in that write up do they say it "rigidly locks"....

I had posted an industry article on the MP3023 Transfer Case, describing its principles of operation, there are no dog clutches in the exploded view of the XFR Case, except for engaging the Planetary Gearset for 4LOW, no description of dog clutches, it's all done with a clutch pack with an electric motor changing pressure on the clutch pack....

With my F150's Tcase, when its put in 4Low an electrical motor meshes gears to ridgidly lock both diff's apparently the same with the WK2.
My XJ's Tcase on the other hand uses a hand lever instead of a motor, to mesh Tcase gears via an internal shift fork.
With both my F150 and XJ, if the shifting procedure is not followed correctly you can actually here gears grinding in those Tcases. Similar to the old clash box manual transmissions that didn't use synchros to mesh gears perfectly at any speed.
What Transfer Case does you Ford F150 have? Not all transfer cases work the same....
Most Transfer cases that are capable of Full Time 4WD, have a differential, with additional equipment to lock that differential if its capable of Part Time 4WD....
The MP3023 Transfer Cases replaces the differential with a wet clutch pack, that pressure is applied by an electric motor and computer controlled to allow more slip as necessary and less slip as necessary.... ...when you shift into 4LOW, it applies full pressure to lock the front/rear driveshafts together so they turn at the same speed....

There is no control the transfer case can apply over the differentials, other than the speed of the driveshafts providing input....

Now in addition to both diffs locked in 4Low it would be great if the rear diff emulates or approaches a mechanical locker.
There's likely electrical driven clutches in the eLSD perhaps for each rear wheel.
Why couldn't both clutches be engaged full time when in 4Low to emulate a locker.
The Diffs do NOT lock in 4LOW, unless you have QDII, and then only the rear eLSD locks...
You just said both Diffs lock, then complain that the Diffs aren't locking..... ....you see, your confusing yourself....
The transfer case locks both front and rear driveshafts to turn at the same speed, it's that simple.....

The eLSD does emulate a locker differential....
There is one differential for 2 wheels on either side of it.... ...this is true of all differentials...
The differential, like an old mechanical LSD, has a clutch pack inside it, that limits slip between the two wheels on either side of the differential....
If you turn up the pressure on the clutch pack with the electric motor, the eLSD will lock.... ....turn down the pressure on the clutch pack, it will limit slip less....
When you shift into 4LOW, if you have an eLSD, the system will turn up the pressure on the clutch pack to lock it.... ....I'm not sure if it will ease up pressure in 4LOW in some conditions...
If you're in Automatic 4WD/4HI, the system will reduce or increase pressure on the clutch pack according to conditions, to limit slip or not limit slip at all, or even lock it.....

There are videos of going extreme cross-axle with the QDII in 4LOW, 2 wheels katty-corner from each other in the air, and they continue to turn smoothly, that can only be accomplished with a lock differential.... ...does it unlock in 4LOW when an unlock differential is better, it might, I just don't know, but I see plenty of evidence it locks when its needed.......
 

·
Registered
Grand Cherokee
Joined
·
3,243 Posts
Jim, until i hear other wise i think you're probably right.
But still in the back of my mind, my persistent lingering question is how does the eLSD actually operate full time in 4Low?
We already know how it operates in 4Hi just like any other LSD diff.
Again, there is an entire thread with a guy that monitored his eLSD with AlfaOBD driving around on the street in Automatic4WD. He stated he was shocked how often the eLSD locked while driving on road, and it varied the clutch pressure often.....

Any other LSD diff, doesn't do that.....

And any other LSD, can break traction in rain and gravel, something the eLSD doesn't do..... ....because any other LSD has only a single torque bias set, that doesn't vary, in some conditions it is too much torque bias, and an open differential would be better....

In 4LOW, I don't know if it stays constantly locked, but there is plenty of evidence it locks when it needs too....

Its so dam hard not having the official Mopar tech. manuals on just whats going on with that eLSD.
And even then, the rear eLSD diff 'might' not have any rebuild detailed diagrams but instead relies on the Jeep techs. to replace the entire diff. as a unit when defective. Don't know!
The Service Manuals have been dumbed down just as much as the Owner's Manual...

2011 WK2 Service Manual said:
The Electronic Limited Slip Differential Module (ELSD) (1) is a microprocessor-based assembly, controlling the rear axle. The ELSD can send 0 to 100% torque from the wheel that is slipping to the other wheel, on the rear axle. The transfer case controls slip from front to rear. The ELSD controls slip from left to right within the rear differential. The ELSD controls an electric motor which drives a gear set which moves a ball ramp to apply force to a wet clutch. This clutch is used to control torque split. Motor position feedback is done with two hall effect sensors on the motor. There is also a temperature sensor on the motor. ELSD will be temporarily disabled with high temperatures on the motor. Communication is via the CAN serial bus. Inputs include: Vehicle speed, Wheel speed, Terrain mode ELSD position sensor, and VIN, odometer for diagnostics. Outputs include: Actual rear differential torque, ELSD status, and PWM control of rear ELSD motor.
The ELSD Module is installed inside the passenger compartment underneath the left side of the rear seat.
 

·
Super Moderator
Joined
·
8,499 Posts
Jim, until i hear other wise i think you're probably right.
But still in the back of my mind, my persistent lingering question is how does the eLSD actually operate full time in 4Low?
We already know how it operates in 4Hi just like any other LSD diff.
My additional guess is that it was probably simpler and more efficient for them to let the ELSD setup work normally and independently from the stuff that engages in 4Low so they could use the same programming for both QT-II and QD-II for 4Low and other SelectTerain features. They are "the same" other than the ELSD when you think about it.
 
21 - 40 of 48 Posts
Top