4WD - Explaining the 3 Systems - Page 2 - JeepForum.com

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post #16 of 33 Old 10-26-2014, 12:44 PM
Bent8
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Just so I'm clear, in QTII auto mode, the front and rear drive shafts are turning under control of a clutch pack which is controlled by a traction computer. The mode selector, under control of the traction computer governs the ratio of slippage in the transfer case front to rear when one of the tires breaks loose.
So if this were the case, in sport mode, the clutch pack would be adjusted to give more traction to the rear than the front possibly causing the rear tires to break away more easily.
Is this, in simple terms, about right?

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post #17 of 33 Old 10-26-2014, 04:14 PM
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Its perhaps simpler than that. The transfer case directly connects the transmission output to the rear axle, no clutch involved, there is no way to disconnect the rear axle. The clutch disks are alternately splined to the front and rear drive shafts and connects the front axle anywhere from 0% to 100% lock. When disengaged no (0%) power is supplied to the front axle, when engaged (100%) its like the common 4WD lock mode. Sport mode probably loosens the clutch pack more than normal mode and therefore makes it feel more like a RWD vehicle. So I guess running in sport mode would cause less clutch wear than normal mode.

Sport mode also adjusts a number of things including stability and traction control and transmission shift points. But yes, if you want to squeal the tires, sport mode is the best one to use.... although if you have a V6 dunno if that helps enough.

Note that the "capability to transfer 100% of power to one axle or the other" description can be misleading. In approximate terms, when there is zero rear axle traction, 100% of the engine power goes to the front axle. When there is zero front axle traction, 100% of the power goes to the rear axle. When all wheels have the same traction, its effectively a 50/50 power mix.

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post #18 of 33 Old 10-26-2014, 04:53 PM
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I think I get it now. The fact that only the front dif is clutch driven is key to my understanding. Thanks for all of the great info!
Al
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post #19 of 33 Old 01-14-2015, 10:22 PM
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Very helpful thread. Jeep does not do a good job explaining the 3 systems.
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post #20 of 33 Old 01-15-2015, 04:26 PM
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Quote:
Originally Posted by ColdCase View Post
They will slip a bit as you go around turns and more if you drive with different size tires on each corner. These kinds of clutches have been used in transfer cases for decades and the only time they seem to be an issue is when they overheat during wildly spinning tire escapades typically in muddy or deep sand conditions. The have a long service life in typical street duty, 200,000 miles plus.
Quote:
Originally Posted by ColdCase View Post
Its perhaps simpler than that. The transfer case directly connects the transmission output to the rear axle, no clutch involved, there is no way to disconnect the rear axle. The clutch disks are alternately splined to the front and rear drive shafts and connects the front axle anywhere from 0% to 100% lock. When disengaged no (0%) power is supplied to the front axle, when engaged (100%) its like the common 4WD lock mode. Sport mode probably loosens the clutch pack more than normal mode and therefore makes it feel more like a RWD vehicle. So I guess running in sport mode would cause less clutch wear than normal mode.

Sport mode also adjusts a number of things including stability and traction control and transmission shift points. But yes, if you want to squeal the tires, sport mode is the best one to use.... although if you have a V6 dunno if that helps enough.

Note that the "capability to transfer 100% of power to one axle or the other" description can be misleading. In approximate terms, when there is zero rear axle traction, 100% of the engine power goes to the front axle. When there is zero front axle traction, 100% of the power goes to the rear axle. When all wheels have the same traction, its effectively a 50/50 power mix.
So in "Auto" mode, no slippage of the clutches unless there is a difference in front and rear wheel speeds. No slippage in "Low" because they are locked together. I still don't understand the "Sport" mode, though, I think. Transmission is "hard linked" to the rear through the xfer case, but "Sport" loosens the clutch-pack. So it CAN spin the rear (if it has enough power and/or low-enough traction), which might cause more wear on the clutches if it happens a lot (say driving down a muddy road in "Sport" all the time -- which would be foolish anyway). But otherwise, the front and rear wheel speeds should be the same, with looser clutch-pressure, so it should reduce the wear over time to the clutches of taking turns and corners (say lots of city driving -- which is going to wear out the vehicle quicker anyway, since I think that qualifies it for the severe-duty cycle of maintenance).

All that sound about right? Sorry for the long post, just wanted to make sure I understand, and it helps me to type through it...
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post #21 of 33 Old 01-15-2015, 04:42 PM
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I thought Sport mode only affected the transmission shifting and had nothing to do with the differentials.

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post #22 of 33 Old 01-15-2015, 07:53 PM
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Quote:
Originally Posted by 2014RedHemiGC View Post
I thought Sport mode only affected the transmission shifting and had nothing to do with the differentials.
The traction control computer puts a little RWD bias in when in sport mode. It also has some affect on the yaw and stability control as well as the throttle response curve. Its more than simply adjusting the transmission shift points.

Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
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post #23 of 33 Old 01-15-2015, 07:57 PM
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Originally Posted by rockspyder View Post
So in "Auto" mode, no slippage of the clutches unless there is a difference in front and rear wheel speeds. No slippage in "Low" because they are locked together. I still don't understand the "Sport" mode, though, I think. Transmission is "hard linked" to the rear through the xfer case, but "Sport" loosens the clutch-pack. So it CAN spin the rear (if it has enough power and/or low-enough traction), which might cause more wear on the clutches if it happens a lot (say driving down a muddy road in "Sport" all the time -- which would be foolish anyway). But otherwise, the front and rear wheel speeds should be the same, with looser clutch-pressure, so it should reduce the wear over time to the clutches of taking turns and corners (say lots of city driving -- which is going to wear out the vehicle quicker anyway, since I think that qualifies it for the severe-duty cycle of maintenance).

All that sound about right? Sorry for the long post, just wanted to make sure I understand, and it helps me to type through it...
I think that sounds about right... if I followed you right... its not clear if there is that much difference in clutch wear, however.

Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #24 of 33 Old 02-18-2015, 08:07 PM
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So is it possible to stick the rear differential from a QD2 onto a QTII? I'm assuming you would need to reflash with the correct program and probably run the extra wire to the back differential...
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post #25 of 33 Old 02-18-2015, 08:19 PM
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So is it possible to stick the rear differential from a QD2 onto a QTII? I'm assuming you would need to reflash with the correct program and probably run the extra wire to the back differential...
No, you need the controller to run it as well, and something to run that controller.
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post #26 of 33 Old 02-18-2015, 10:23 PM
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There is a QD control module and perhaps some wiring. Then you need to convince a dealer to add the QD option to the VIN and flash the update, perhaps similar to what they do to activate the trailer harness. Dunno if thats possible or if anyone ever tried it.

Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
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post #27 of 33 Old 08-15-2015, 04:13 PM
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Does the QT-I have a high and low range?

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post #28 of 33 Old 08-15-2015, 04:57 PM
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Does the QT-I have a high and low range?
No
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post #29 of 33 Old 03-02-2017, 09:56 AM
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Quote:
Originally Posted by loveracing1988 View Post
Note that Rock mode doesn't use the clutches, 4 low has to be engaged to go into rock mode so it is spline locked. The other modes sets how the power is distributed from the start. Snow and mud mode for example sets the torque split to 50/50.
Because of the way the transaxle shifts the clutch pack is locked before the splines for 4Low (planetary gear set) are engaged. Dunno if this transfer case actually splines the chain gear as a typical case may or if the front axle power always goes through the clutch pack but there should be no clutch slip unless the clutches are way worn. Power to the rear axle never goes through the clutch pack.

Its the same setup as the earlier automatic transfer cases used in the WK2, just the shift motor, sensors, and some pieces are in different places and made in a different factory.

Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #30 of 33 Old 03-03-2017, 09:38 AM
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Quote:
Originally Posted by LuckRider View Post

Quadra-Drive II

Features:

* Fully automatic, high range for year round driving in all conditions
* Active electronic transfer case and rear electronic limited slip differential
* When traction is lost torque can be sent to wheel or wheels with the most traction
* System works progressively and on-demand
* Works together with brake traction control
* Torque can be sent front to back or side to side
* 4 Low mode locks front and rear driveshaftsfor low speed power/rock crawling or towing
* Includes Selec-Terrain
* Neutral position for flat towing
* Hill Descent control, controls speed to a set mph without driver input.
* Select-Terrain provides traction programs for various situations, like mud, snow, sand, rock. The selections change from year to year. Check your owners manual for detail.


Operation

The QD II uses the same setup as the QT II plus a locking/limited slip rear differential. BTC or BLT is not used on the rear axle. By using a limited slip diff, the QD II provides a more solid foundation for transferring the torque (because it is a set of gears forcing the power to be transferred rather than brakes locking wheels which can be overridden). This system also comes with hill decent control which automatically applies the brakes for a slow controlled descent down steep terrain. When one mashes the throttle on a QD vehicle, the traction controller locks the rear diff and thus provide superior launch traction.

BCT or BLD converts engine power to heat in the brakes, not so good for stoplight to stoplight performance, rock climbing, or for heavy duty mud bog abuse where you need as much power as the engine can deliver. The QD axles and transfer case allows much more power to reach the road.

The STR8 uses a QD system, but the transfer-case does not have low range.

Edit: Updated by ColdCase March 2 2017
Hey ColdCase,

Can you update the QDII for the 2017+ TH. It uses Selec-Speed for both low speed crawling, hill start assist, and hill descent. It doesn't have the hill-descent button.
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