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Unread 12-11-2010, 07:26 PM   #1
jeepsterguy
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QTII vs QDII

The only difference I see between the two systems is the rear LSD.
Considering that JEEP believes that we don't need a front LSD due to braking action that will stop a spinning front wheel, why do we need a rear LSD (clutch type I was told, that will eventually wear out the clutches)? A lot easier to replace brake pads/rotors.
Just wondering.

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Unread 12-11-2010, 08:18 PM   #2
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Unread 12-12-2010, 02:22 AM   #3
Marcus86GLHS
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well if you are doing serious rock crawling and deep mud adventures every litle bit of extra traction is going to be needed, hence, locking differentials are beneficial. on snow and ice? not so much, but still a good thing to have. it is puzzling to me why the 2011 doesnt have a locking front diff, i bet it will in coming years.
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Unread 12-12-2010, 08:27 AM   #4
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Quote:
Originally Posted by Marcus86GLHS View Post
well if you are doing serious rock crawling and deep mud adventures every litle bit of extra traction is going to be needed, hence, locking differentials are beneficial. on snow and ice? not so much, but still a good thing to have. it is puzzling to me why the 2011 doesnt have a locking front diff, i bet it will in coming years.
http://www.youtube.com/watch?v=nIapRCQobKA&NR=1

In this video it looks like the brakes do a pretty good job.
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Unread 12-13-2010, 06:20 AM   #5
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The difference is between simply slowing a wheel that is spinning (the braking action of the traction control system) and transferring the torque of the wheel that is spinning to the lateral wheel that is not spinning. Forward energy is lost with the braking, while it is transferred to other wheels with traction with the LSD.

As for the implications of this, it depends on the situation. As the poster above said, it may not be very useful under certain circumstances--snow and ice perhaps. But, an important thing to remember is that the LSD does not hinder the traction control system that works with brakes. That system is still free to operate, which means that if you are in a situation where the torque transfer to the lateral wheel with traction (by the LSD) actually causes it to slip, then you still have the braking action of the TCS/ESC. The LSD is not a substitute, but an additional feature.

As I've mentioned before, the LSD is not exclusively and off-road feature. Sports cars, for example, rarely come without them. Torque transfer to an outer wheel in a curve, if needed, provides stability while maintaining forward momentum to a degree not possible with the simple braking action of a stability assist system.

As for potential issues with the clutch in the LSD, obviously, the more you use it, the more wear it will get. But, my sense is that LSD technology is well-established and longevity is not the problem that it might be with other "added features." A completely new ELSD may have some electronic issues to be sorted out, but hopefully that could be done with software updates, which aren't invasive.

I'll say it again, even the base QTI should have LSDs. They are a safety feature, and they enhance handling, even if you never go off-road.

BR
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Unread 12-13-2010, 11:47 AM   #6
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Take care of the ELSD and it will take care of you for a long time. I'm nearing 100,000 miles on mine and they're still working well.
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Unread 12-13-2010, 01:48 PM   #7
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Quote:
Originally Posted by jeepsterguy View Post
In this video it looks like the brakes do a pretty good job.
That's actually a pretty good vid,it visually explains everything for those who don't see how it works.
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Unread 12-13-2010, 08:55 PM   #8
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Quote:
Originally Posted by Burb_Rated View Post

I'll say it again, even the base QTI should have LSDs. They are a safety feature, and they enhance handling, even if you never go off-road.

BR


A front LSD is great on the trail, but an exception arrises on dirt 'softroads', or on pavement. With enough HP, a front LSD can introduce 'push' as the front outside wheel tries to accelerate and steer. I have a highly modified allroad (500 hp 87 octane, 800 hp on race gas). It has a custom rear-biased torsen center and LSD rear, and I opted against putting an LSD in the front because I wanted to have power oversteer when cornering. If the front had an LSD, it would tend to push and understeer.

Lighter cars like the WRX STi work OK with LSD's in front, but in heavier cars with softer suspensions, LSD's can wash out the grip on the outside front tire when cornering and accelerating.

In other words, I would think Jeep would offer a front LSD in the Overland, but not in the SRT8 version. For serious offroading, LSDs are far superior to brake systems.

All that said, some pretty crazy adventures have been had with no LSDs front or rear... (If you aren't compelled to read this entire story in one sitting, you probably don't need a Jeep anyway)

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Unread 12-13-2010, 09:58 PM   #9
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Quote:
Originally Posted by Sarge_ View Post
A front LSD is great on the trail, but an exception arrises on dirt 'softroads', or on pavement. With enough HP, a front LSD can introduce 'push' as the front outside wheel tries to accelerate and steer. I have a highly modified allroad (500 hp 87 octane, 800 hp on race gas). It has a custom rear-biased torsen center and LSD rear, and I opted against putting an LSD in the front because I wanted to have power oversteer when cornering. If the front had an LSD, it would tend to push and understeer.

Lighter cars like the WRX STi work OK with LSD's in front, but in heavier cars with softer suspensions, LSD's can wash out the grip on the outside front tire when cornering and accelerating.

In other words, I would think Jeep would offer a front LSD in the Overland, but not in the SRT8 version. For serious offroading, LSDs are far superior to brake systems.

All that said, some pretty crazy adventures have been had with no LSDs front or rear...
I have a Cherokee with front and rear Truetrac LSDs, I like them.
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