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Unread 03-06-2011, 02:36 AM   #1
LuckRider
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4WD - Explaining the 3 Systems

Here is an explanation of the 3 4WD systems that are used in the WK2. One is technically an AWD system, but we will not berate Jeep for calling it a 4x4 because the system uses magic sauce to make it the most capable AWD many have seen (more capable than many 4x4 systems on the market). The same components are used in all model years 2011-2014.

The order that follows is from least capable to the most capable. As always, feel free to comment or suggest improvements. This as a living guide that is changed and updated to integrate suggestions and to match the current WK2 capabilities.

The availability of one system over another varies from year to year. For example, some years Laredos can get QD, other years not. QD is only available on V8s and Diesels, however. wk2jeeps.com has a pretty good index of whats available year by year. It doesn't list those periods of times one option was restricted due to parts availability.

Quadra-Trac I

Features:

* No shift lever or driver interaction required.
* Full-time 4-wheel drive provides smooth operation and vehicle stability under all conditions because torque is constantly being transferred.
* Torque distribution provides traction to maintain forward motion under most conditions.
* The Brake Traction Control System (BTCS) works in tandem with full-time 4 wheel drive. BTCS provides resistance to any wheel that is slipping to allow additional torque transfer to wheels with traction.
* Robust design and improved sealing enhance reliability.
* No maintenance required.


Operation:

As mentioned above, this is a single speed transfer case that offers no locking center differential (part time 4wd setting usually known as 4 High on vehicles like the Wrangler). This allows the system to be used on the road in any conditions and traction quantities. In order to supply power to the wheels that do have traction, the ABS sensors determine when a wheel is slipping and apply the brakes to that side.

The differentials and transfer-case of the QTI are open. This means that the wheels are all allowed to spin at any speed regardless of the power being sent or the speed of the other wheels. If one wheel were to loose traction, all power would go to that wheel, and you would be stuck. With Brake Traction Control (BCT) (Jeep marketing likes to use the term Brake Locking Differentials (BLD) ), the ABS system detects when a wheel is spinning faster than the other wheels and applies the brake to that wheel. By applying the brake, it forces resistance to that wheel which allows the power to be sent to other wheels that have more traction.

These brake locking differentials do a great job of moving the power. Here is a perfect video of it in action on a patriot (different 4wd system, but it is still making the climb because of the BLD). Watch the tires of both the passenger and driver's sides to see when the brakes grab:


Because the differential is open, it is always changing the amount of torque that is being sent to the front and rear drive shafts. Some sources say that the split is 48/52 where 52% of the power is going to the rear to give the Jeep a sportier feel. One site claims that the split happens to be 50/50. According to the Jeeps website (http://www.jeep.com/en/4x4/how_syste...k/quadra_trac/) The system just transfers torque as necessary.

Quadra-Trac II

Features:

* Active, on-demand four-wheel drive requires no driver input.
* Instantly anticipates slip and preemptively redirects torque as needed.
* Vehicle stability under all conditions because torque is constantly being transferred.
* 4WD Low operation mode provides an advantage over vehicles equipped with a single-speed all-wheel drive transfer case.
* Electric shifting between 4WD Auto and 4WD Low provides smooth operation and improved NVH control compared to systems with mechanical linkage.
* Enhanced traction and stability provided by the Traction Control and Electronic Stability Program (ESP) working in tandem with four-wheel-drive.
* A robust design and sealing for reliability.
* Maintenance-free.
* A neutral mode permits 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 basics of this 4wd system are similar to those of the QT I, however, they add a locking transfer-case. Inside the transfer case is an electronic clutch pack that has the capability of transferring 100% of the power to either the front axle or the rear axle depending on which one has more traction. The QT II also offers low range and neutral position. The neutral position allows you to flat tow the vehicle. With the low range, the torque is multiplied by 2.72. This extra 2.72:1 gearing provides the extra power needed to traverse more difficult terrain. When the system in in 4 low, the transfer case locks the front and rear drive shafts together so that both axle gets an equal amount of torque. This system also comes with hill descent control which automatically applies the brakes for a slow controlled decent down steep terrain.


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 Jan 15, 1015

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Unread 03-06-2011, 11:25 AM   #2
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QTII also has hill descent.


In a nutshell:

- QTI = AWD. Front-to-rear and side-to-side differentials are open requiring electronic braking to control wheel spin;

- QTII = QTI plus front-to-rear differential has an electronic clutch and can lock and a low range. The electronics include hill descent and the auto-terrain functions for snow, sand, etc. Side-to-side diffs are still open;

- QDII = QTII plus a rear side-to-side differential with an electronic clutch. Front side-to-side diff is still open.

BR
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Unread 03-25-2013, 06:41 PM   #3
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So, if a vehicle is equipped with Select-Terrain, can one assume it has QD-II? I'm a little confused.
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Unread 03-25-2013, 06:58 PM   #4
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If the vehicle has the select terrain knob then it has a Quadra Trac II transfer case (QTII).

Quadra Drive (QD) is another option on top of QTII.
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Unread 03-25-2013, 11:09 PM   #5
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Just a note of clarification (if QD is important to you). You could never get a QD on a V6. It was and is only available with the V8, perhaps the CRD. The QD and QL association changed over the years, however. You could get QD without QL, but you probably need to be looking at early 2011s. QD was restricted to overlands later in 2011 model year (by that time all overlands had QL) and the options changed a bit in 2012, and then again in 2014. Basically all ORAIIS with V8s or diesels have QD. It has become a stand alone option on V8 Overlands, seems still to be standard on Summits and SRT8s.

From Jeep's features and availability descriptions:

"Off Road Adventure II — Includes Quadra-Drive 4WD system (V-8 only), two-speed on-demand transfer case, Selec-Terrain, Quadra-Lift air suspension system, Trail Rated badge, full-size spare tire, steel spare wheel, P265/60R18 OWL on/off-road tires, Skid Plate Group"

QL is great if you don't want to compromise highway handling or off road clearance (it adjusts). If you don't mind the highway compromise a lifted vehicle and larger tires performs well off road. QL may not be for you. It is nice to have some choices, however, as we do drive in a lot of different conditions.
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Unread 04-30-2014, 05:11 PM   #6
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QTII does not transmit 100% power to the tire with most traction, it will transmit 100% power to the axle with most traction, then BTC takes over, which is about 50% efficient in getting power to the tire with traction... which is much better than nothing. As far as improvement over QTI, tires will make more of a difference. QTII will be better than QTI in situations where low range is useful, and there can be many of them. If you run the numbers, assuming only one tire has traction, QTI will get 25% of engine power to it, QTII 50%. How that transfers to the street depends, but its a useful number for rock climbing.

The comparison words is referring to previous generation WKs. But they just say the transfer case is proven in that is has survived their testing and is efficient, but does not say efficient compared to what. I would expect little difference between QTIs over the years, but the newer ones are lighter and run lower weight oil... so maybe you'll get a 0.1 mpg improvement As far as QTI compared to QTII, there is a weight increase and some clutch drag... but you are talking tenths of a mpg not one or two.

GM uses the same case in many of its light trucks.


The WK2jeeps site is very good in general but pretty much quotes the Jeep 4x4 corporate stuff.. which can be misleading and lacks the detail you need for a thorough understanding.
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Unread 05-02-2014, 01:44 PM   #7
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If you scroll down to the bottom of the wk2jeeps page it will go through the contents of the option packages.

For example, The 2014 V6 Laredo All Weather group included QTII and was a much more popular option than the ORAs I think.

All 2014 V8s, Laredo X or otherwise, came with QTII.


Off Road Adventure Group I (Laredo 4WD and Limited 4WD)

P245/70R17 OWL On/Off Road Tires (Laredo)
P265/60R18 OWL On/Off Road Tires (Limited)
Hill Descent Control
Quadra-Trac II 4WD System (Laredo)
Selec-Terrain System
Skid Plate Group (Fuel Tank, Transfer Case, Front Suspension, Underbody)
Spare Tire, Full Size with Steel Spare Wheel
Tow Hooks
Trail Rated Badge


Off Road Adventure Group II (Overland)

18x8.0" Aluminum Polished Wheels
P265/60r18 Owl Michelin On/off Road Tires
Skid Plate Group (Fuel Tank, Transfer Case, Front Suspension, Underbody)
Tow Hooks
Trail Rated Badge


All-Weather Capability Package (Laredo 4WD V6)

Daytime Running Lamps
Engine Block Heater
Hill Descent control
Quadra-Trac II 4WD system
Remote Start
Selec-Terrain system
Slush Mats & Cargo Liner
Tow Hooks


5.7L VVT Hemi with MDS

220 Amp Alternator (Overland 4WD)
230mm Rear Axle (all 4WD models)
3.45 Rear Axle Ratio (all models)
Anti-lock 4-wheel Disc HD Brakes (Limited, Overland 4WD)
Dual Bright Exhaust Tips (all models)
Dual Rear Exhaust (all models)
Electronic Limited Slip Rear Axle (Overland 4WD)
Heavy Duty Engine Cooling (Overland 4WD)
Hill Descent Control (Laredo X)
Quadra-Drive II (Overland 4WD)
Quadra-Trac II (Laredo X)
Selec-Terrain (Laredo X)
Trailer Tow Group IV (Overland 4WD)
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Unread 05-04-2014, 07:25 AM   #8
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Sport mode adjusts the transfer case clutches for a more rear wheel drive feel. It also changes the transmission shift points to be more responsive. If you have QL, it lowers the suspension to aero mode.
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Unread 10-25-2014, 06:37 PM   #9
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Qtii

Little confused on the clutches in the open transfer case. I drive in "auto mode". Will this cause excessive wear on the transfer case clutches? How about sport mode?
Do these clutches slip in normal driving?
Thanks , Al
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Unread 10-25-2014, 06:52 PM   #10
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Quote:
Originally Posted by Bent8 View Post
Little confused on the clutches in the open transfer case. I drive in "auto mode". Will this cause excessive wear on the transfer case clutches? How about sport mode?
Do these clutches slip in normal driving?
Thanks , Al
The only way the clutches slip is if there is a speed difference between the front and rear axles. So under normal driving you have nothing to worry about.
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Unread 10-25-2014, 11:36 PM   #11
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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. They have a long service life in typical street duty, 200,000 miles plus.
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Unread 10-26-2014, 07:06 AM   #12
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There is a short article in Gears magazine. Note that this transfer case is also used by GM in light trucks.

http://www.gearsmagazine.com/magazin...aece66d#page36

Transmission Digest also had an article but can't find it now.
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Unread 10-26-2014, 11:01 AM   #13
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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.
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Unread 10-26-2014, 11:13 AM   #14
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So when you say "spline locked", there would be direct drive in the transfer case in rock mode. The slippage would occur in the front and rear open difs in QTII. Correct?
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Unread 10-26-2014, 11:23 AM   #15
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Quote:
Originally Posted by Bent8 View Post
So when you say "spline locked", there would be direct drive in the transfer case in rock mode. The slippage would occur in the front and rear open difs in QTII. Correct?
It would quite be direct drive as there is a gear reduction in the transfer case in low range but yes, the slippage would only be at the tires in 4 low.
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