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  #85  
Old 10-14-2010, 05:33 PM
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Re: No front ELSD for QD II?

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Originally Posted by chibianh View Post
In the grand cherokee chat yesterday, this question was brought up again, too.. here's what they answered.
it is interesting, how we automatically think elsd is better on the front, but we have no data whatsoever to back that up.....it seems like locking is better but may not really be......

a front elsd would have to be considerably de-tuned to not lock on pavement relative to a rear.....this would invaribly delay response time in the event of traction loss.....

i think landrover has no front elsd......

i am sure there are situations where elsd might be better and vice versa .....none of the elsd fully locked anyway.....so i can totally see the new system being better, esp with different behavior for different terrain types, with the terrain select........

if you want a fully locking system get a rubicon......fully locking does not provide as good of traction on loose surfaces(snow, sand, mud,slippery streets) as a smarter system such as qdII......rock crawling boulders at .2 miles per hour fully locked is probably better......the wk2 needs to have the best traction in the most likely situations a customer will encounter.... why would i want a traction system that worked best in a driving situation i rarely encounter
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  #86  
Old 10-14-2010, 06:12 PM
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Re: No front ELSD for QD II?

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Originally Posted by chibianh View Post
In the grand cherokee chat yesterday, this question was brought up again, too.. here's what they answered.

Quote:
With regard to front ELSD, we developed our Quadra-Drive II system with a variable t-case, rear ELSD, better BLD performance and larger brakes to provide better traction performance than our prior system with ELSD.

Quote:
The combination of the variable T-case, air suspension, ELSD, and BLD's allowed us to optimize traction performance and ground clearance. We conducted significant tests (in all environments) comparing the 2011 Jeep Grand Cherokee to prior models to ensure we delivered.
IMHO these quotes are techno-babble with no evidence. As an engineer, I think they are also incorrect from a technical viewpoint. They can't get around the torque loss for the traction wheel introduced by brake use.
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Old 10-14-2010, 06:39 PM
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Re: No front ELSD for QD II?

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Originally Posted by suvowner View Post
........

if you want a fully locking system get a rubicon......fully locking does not provide as good of traction on loose surfaces(snow, sand, mud,slippery streets) as a smarter system such as qdII......rock crawling boulders at .2 miles per hour fully locked is probably better......the wk2 needs to have the best traction in the most likely situations a customer will encounter.... why would i want a traction system that worked best in a driving situation i rarely encounter
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  #88  
Old 10-14-2010, 07:58 PM
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Re: No front ELSD for QD II?

I may be changing my mind on this subject. Last week I was in Moab for 4 days of trails with my WK. The second day my right front wheel speed sensor went out - which I think means at the very least that my front ELSD wasn't working or was working suboptimally. I was stuck only once - on a very steep and somewhat rutted incline on Fins and Things and I think I could have made that with a bit more go pedal. I made it through Golden Spike's Crack barely chirping tires and the Golden staircase was a piece of cake. I think if the WK2's front traction is at least as good as my sick WK's front traction was, I'd be happy with the performance.
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Old 10-14-2010, 08:58 PM
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Re: No front ELSD for QD II?

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Originally Posted by vonk View Post
IMHO these quotes are techno-babble with no evidence. As an engineer, I think they are also incorrect from a technical viewpoint. They can't get around the torque loss for the traction wheel introduced by brake use.
they say significant tests........unless they are lying there must be data from those tests.....

yes, but just how critical is some torque loss to a front wheel in most reduced traction situations....i guess, on a steep incline, with only the left front wheel with traction, would the available torque to that one front wheel be enough to move the vehicle ??? would it be enough with the elsd, b/c remember the elsd could never really fully lock and give truely all the torque anyway...

in most other frequently encounterd situations, the faster reacting terrain select is probably better on the front.....
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Old 10-15-2010, 06:16 AM
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Re: No front ELSD for QD II?

This is an interesting thread....and it seems to me that Jeep decided to make the new QDII system almost exactly like the 4wd system that's been on the 4Runner since 2003. As the owner of a 2004 4Runner, I can tell you that the 4wd system works very well in just about any on-road or off-road and especially good in deep snow.

The Toyota system uses what they call ATRAC as a brake-based system and also has a fully locking center differential. It works incredibly well in snow and I've used my 4Runner to get me up to my winter cabin plenty of times. That's saying a lot because there are very few SUVs with a good enough 4wd system to make it up the steep path when there is snow on the ground.

And since the 2009 model year (and carrying on through the new generation 4Runner in 2010) the Trail Edition 4Runner also has an electronically locking rear differential. I obviously don't have it on mine, but most guys say they don't even need it because the ATRAC works so well.
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Old 10-15-2010, 06:00 PM
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Re: No front ELSD for QD II?

Interesting new points being made.

Think about this also: If you're going uphill, the weight is obviously shifted rearward, increasing traction where the ELSD is. If you're going downhill, you have gravity helping you move, and need traction primarily for braking. You will almost always have traction on at least one rear wheel, even in crawling situations.
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Old 10-15-2010, 08:19 PM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by RedRocker View Post
I may be changing my mind on this subject. Last week I was in Moab for 4 days of trails with my WK. The second day my right front wheel speed sensor went out - which I think means at the very least that my front ELSD wasn't working or was working suboptimally. I was stuck only once - on a very steep and somewhat rutted incline on Fins and Things and I think I could have made that with a bit more go pedal. I made it through Golden Spike's Crack barely chirping tires and the Golden staircase was a piece of cake. I think if the WK2's front traction is at least as good as my sick WK's front traction was, I'd be happy with the performance.
Thanks for posting your real world experience here, even if it is for your sick WK.
As more people get a chance to test the traction of their WK2s on various surfaces we can get a good set of experiences posted.
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  #93  
Old 10-19-2010, 05:38 PM
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Re: No front ELSD for QD II?

Lets say you are going up a steep driveway in fairly deep snow. Don't you think both front wheels putting power to the ground without the brake would be better than one wheel with the brake in an attempt to force the other to move?

If not... I suspect you like ABS as well.
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Old 10-19-2010, 07:05 PM
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Re: No front ELSD for QD II?

When going up a steep driveway, the lion's share of traction will be in the rear. An ELSD is not going to put power to the ground through both wheels if one of them has no traction. It doesn't create traction where none previously exists.

So the statement "both front wheels putting power to the ground without the brake would be better than one wheel with the brake in an attempt to force the other to move" doesn't actually make sense for comparison. If you can put power down through both wheels, then you're not actually in a situation where the brake-induced traction control would be doing anything.

The ELSD and the brake based TC are both active in the same scenarios: when traction is reduced or lost at one wheel. If the brake-induced traction control system is quick and well tuned enough, it will result in the same thing: continued delivery of torque to the wheel with traction. The only drawback of course is a reduced amount of torque. But if you consider that it's only one corner of the car that can be affected by this at one time (since the rear has the ELSD), the loss of effective torque and power to be used in climbing the hill will be quite minimal.
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Old 10-19-2010, 09:43 PM
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Re: No front ELSD for QD II?

Quote:
Originally Posted by Kev- View Post
Interesting new points being made.

Think about this also: If you're going uphill, the weight is obviously shifted rearward, increasing traction where the ELSD is. If you're going downhill, you have gravity helping you move, and need traction primarily for braking. You will almost always have traction on at least one rear wheel, even in crawling situations.
also, i think the center diff/transfer case will lock....if so, then the front diff cant turn faster than the rear diff, which would control wheel spin on the front as well....ie no front wheel could turn faster than a rear wheel.....

http://www.jeep.com/en/4x4/how_syste...uadra_drive_2/

notice the error regarding front and rear locking diffs.....
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