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  #37  
Old 09-01-2010, 08:32 PM
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Re: No front ELSD for QD II?

Yes they are Scott.

My interest lies in finding out exaclty what the diifs are. My hunch is that they are Mercedes diffs with electronics added to produce what Jeep is terming a "locker", when in fact it isn't. It's traction control based torque transfer.

In my experience, vehicles utilising traction control by way of input from ABS sensors that then use the brake caliper to bind the spinning wheel therefore transfer torque across the axle to the opposing wheel are at a distinct disadvantage in many situations, most notably soft sand.

Imagine the situation in soft sand, moving off from a standing start, one front wheel begins to slip, the brake caliper brakes the slipping wheel transfering drive to the opposite side. As the torque is applied to this wheel, is slips a little, which sends the computer into thinking about to spin hopelessly,whereby it then sends the drive back to the opposite wheel! You end up with torque being transferred from side to side, and the vehicle progressively bogging itself.
Most unsatisfactory if that's the case.

But, regardless, we're still yet to find out exactly the sytem that Jeep is running.... Mr Jansen, come on down!
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  #38  
Old 09-01-2010, 08:41 PM
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Re: No front ELSD for QD II?

sept 8, 2010 at 6 pm we will know the answers to all this
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  #39  
Old 09-01-2010, 10:46 PM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by Jim Hef View Post
Now that the Forum is back up and running, let's go further on this. From How Stuff Works:
"The locking differential is useful for serious off-road vehicles. This type of differential has the same parts as an open differential, but adds an electric, pneumatic or hydraulic mechanism to lock the two output pinions together.

This mechanism is usually activated manually by switch, and when activated, both wheels will spin at the same speed. If one wheel ends up off the ground, the other wheel won't know or care. Both wheels will continue to spin at the same speed as if nothing had changed."

That's what I was referring to as a "locker" diff...equal power to both wheels whether they are off the road/trail or not. What we need to get info on is what this electronically activated diff is doing...locking, or limiting the slip to one side or the other depending upon which wheel has more traction.
Agreed, but torque and power must not be confused. Torque is much like force that can only be applied where it finds an equal and opposite reaction. Similarly, torque can only be applied where it finds resistance. Therefore, the airborne wheel of a locked axle sees no torque. Itís all applied to the resisting wheel on the ground.

As for the ELSD, the carís computer senses speed differences between the right and left wheel of an axle. If such a difference increases too quickly (onset of wheel spin), the computer sends a signal to the ELSD to compress the clutch-pack (that connects the axle shafts) until the speed difference disappears. But, sensing that, the computer immediately releases the clutch-pack pressure until a speed difference reoccurs, whereupon the clutch-pack is re-clampedÖ..and so on in rapid cycles, just like the ABS does it. The average result is like a locked differential in which the torque is automatically distributed between the wheels according to how much traction (resistance from the pavement) each wheel has.
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  #40  
Old 09-01-2010, 11:28 PM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by RedRocker View Post
I kinda wonder why they chose to put the ELSD in the rear. In my experience pulling was more effective than pushing, so when adding a locker/lsd you'd add to the front before you'd add to the rear. For snow - front wheel drive is better than rear wheel drive, so why wouldn't a front ELSD be better than a rear ELSD? Unless the front axle on the WK2 is totally different than the front axle of the WK1, they already had a front solution - why put money into developing a new rear ELSD axle?
My hunch:

Plan A:

The 2010 QD-II system has hydraulically controlled ELSDs in front and rear. The inherent response lag of these ELSDs limits their integration with some features of the carís electronic stability control. So for 2011, Jeep looked around for a quicker ELSD and found a magnetically controlled differential. It eliminates the unwanted response lag, and needs no external plumbing. Now they could fully integrate the ELSDs with the carís computer controlled dynamic stability system.

For the 2011 rear axle, Jeep would purchase the new differential, case and all, from the manufacturer. But in front the real estate is crowded, requiring a special differential case. If the new manufacturer had no drop-in unit, somebody had to redesign something and that spells lead time. Meanwhile the 2011 cars had to go into production.

Plan B:

Until the new ELSD front installation is available, Jeep could put the new ELSD in back and a provisional differential in front. But staying with the 2010 front ELSD would require extra electronic control and some external plumbing. A self-contained, self-acting LSD was needed. Use the Vari-Loc LSD.
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  #41  
Old 09-09-2010, 12:07 AM
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Re: No front ELSD for QD II?

Lets say the snowplow came through and plowed the end of your driveway shut.... you creep up to it then try to push through and one of your front wheels starts to spin...

Which would you prefer:
1. The brakes stop the first wheel from spinning creating unneeded drag and load.
2. Both wheels spin without the use of any brakes and the truck pulls itself through.
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  #42  
Old 09-09-2010, 12:23 AM
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Re: No front ELSD for QD II?

#2 please! But you kinda loaded the questions
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  #43  
Old 09-09-2010, 06:07 AM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by Jeff_Jeske View Post
Which would you prefer:
1. The brakes stop the first wheel from spinning creating unneeded drag and load.
2. Both wheels spin without the use of any brakes and the truck pulls itself through.
I think they use the ABS to keep the first spinning wheel at the same speed as the other, creating a pseudo-locked axle.
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  #44  
Old 09-09-2010, 08:28 AM
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Re: No front ELSD for QD II?

In the engineering chat we learned that thereís no more front ELSD in QD2 for 2011. Instead, the ABS system is used for slip control. So, do they still lock the front axle in 4low? If one wheel becomes airborne while rock crawling uphill, using the ABS to hold it would rob the traction wheel of 50% of available torque.
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  #45  
Old 09-09-2010, 10:36 AM
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Re: No front ELSD for QD II?

No Vonk, the diffs NEVER locked whether in 4Lo or not, QD or not! 4Lo locked the transfer case to deliver 50/50 front and rear...that's it!
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  #46  
Old 09-09-2010, 12:01 PM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by Jim Hef View Post
No Vonk, the diffs NEVER locked whether in 4Lo or not, QD or not! 4Lo locked the transfer case to deliver 50/50 front and rear...that's it!
Then how did they handle the airborne wheel situation? Didn't Jeeps have lockable diffs long before ABS/ELSD involvement?
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Old 09-09-2010, 01:58 PM
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Re: No front ELSD for QD II?

Only as an aftermarket replacement for the diff...air locker comes to mind. The airborne wheel has brake application, causing the power to be sent to the on-ground wheel. 4wd is a misnomer in any of these systems...one wheel front and rear gets power at any one time.
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  #48  
Old 09-09-2010, 05:24 PM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by Jim Hef View Post
Only as an aftermarket replacement for the diff...air locker comes to mind. The airborne wheel has brake application, causing the power to be sent to the on-ground wheel. 4wd is a misnomer in any of these systems...one wheel front and rear gets power at any one time.
Well, if this is so, then I was dreaming all along about a much more sophisticated drive line than what, according to your declaration, Iíll get with my Overland.

But, could you elaborate about the misnomer? Iím confused.
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