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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.

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 May 4 2014

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Unread 03-06-2011, 06:56 AM   #2
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If you go to the Jeep site under capabilites...it explains with video.

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

The link is for Quadra drive II but on the left hand side there are links for all systems.
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Unread 03-06-2011, 08:48 AM   #3
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Great info! Thanks!
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Unread 03-06-2011, 11:25 AM   #4
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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.

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Unread 03-06-2011, 12:07 PM   #5
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Is QDII available on all models or only Overland?
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Unread 03-06-2011, 12:34 PM   #6
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Quote:
Originally Posted by WK2011 View Post
If you go to the Jeep site under capabilites...it explains with video.

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

The link is for Quadra drive II but on the left hand side there are links for all systems.
I linked one of those in the first post. Honestly, they don't give a good enough representation of what is going on. That is why I created the thread.

Quote:
Originally Posted by Burb_Rated View Post
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 for 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
Yeah, I forgot to add hill decent for QT II. Look at the time I posted
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Unread 03-06-2011, 01:39 PM   #7
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Quote:
Originally Posted by TheProfessional View Post
Is QDII available on all models or only Overland?
According to the Jeep website it's optional on the Laredo X, Limited and the Overland. Also it only comes with the V8. I have it on my Overland.
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Unread 03-06-2011, 08:34 PM   #8
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Quote:
Originally Posted by WK2011 View Post
According to the Jeep website it's optional on the Laredo X, Limited and the Overland. Also it only comes with the V8. I have it on my Overland.
Thanks. Their online configuration tool leaves a bit to be desired.
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Unread 03-25-2013, 06:41 PM   #9
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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   #10
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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, 07:01 PM   #11
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Never mind. ColdCase got it.
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Unread 03-25-2013, 07:36 PM   #12
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Thanks

Quote:
Originally Posted by ColdCase View Post
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.
Thanks! Thought so but wanted to make sure. Have been scoping out WK2s for about 3 months and am waiting for the right one to come along, (V6 Laredo X, QTII or QDII, Nav and Heated Leather w/Sunroof, pref w/ ORAI). Plans are lift and tires w/ stock wheels. Have been watching the forum and trying to learn but haven't participated until now.
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Unread 03-25-2013, 08:04 PM   #13
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Quote:
Originally Posted by illflo View Post

Thanks! Thought so but wanted to make sure. Have been scoping out WK2s for about 3 months and am waiting for the right one to come along, (V6 Laredo X, QTII or QDII, Nav and Heated Leather w/Sunroof, pref w/ ORAI). Plans are lift and tires w/ stock wheels. Have been watching the forum and trying to learn but haven't participated until now.
Laredo does not have the QD2 option. Only QT1 and QT2. ORA 1 is equipped with QT2 only. ORA2 is equipped with QD2 only. Limited and above have the option for ORA2. QD2 has quadralift which cannot be lifted aftermarket.

Have you built the GC on Jeeps website? some features you want are not on Laredos.

Sent from my underground lair.
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Unread 03-25-2013, 08:13 PM   #14
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Quote:
Originally Posted by Jackal01 View Post
Laredo does not have the QD2 option. Only QT1 and QT2. Ora 1 is equipped with QT2.

Sent from my underground lair.
Interesting. So if you get a Laredo or Laredo X w/ ORA1 it can't be equipped with QD2? Now I'm really confused. From (just) reading Jeep's website, it seems they would have you believe you can only get QDII w/ ORAII which is ORAI (skid plates, tow hooks, etc.) with air suspension, right? Or am I confused about this too? To complicate the matter further, it looks like (from my aforementioned brief perusal of Jeep's site) the only way to "build" one on the Jeep site w/ ORAII is to get a 5.7. Now I'm really confused. Help!
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Unread 03-25-2013, 08:21 PM   #15
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Jackal,

Doh! After re-reading your post a couple times and checking out the site, it seems you are correct, Laredo's can get ORA1 (tow hooks & skid plates) and QTII, and I'm chasing my tail. ORAII is Air lift + ORAI and QDII. Thanks for the help, and Alice is pretty sweet.
If you have QT-II, does your in-dash display show "Jeep" after startup or something different? I know from a test drive that QDII-equipped ones display "Quadra-Drive".
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