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Budd Stanley & Chrysler
Chryslers 4WD Systems
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Budd Stanley & Chrysler
Chryslers 4WD Systems
Both the Renegade and Wrangler are considered 4WD’s, however they have very different ways to direct torque to all four wheels.
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Budd Stanley & Chrysler
Chryslers 4WD Systems
The Wrangler's traditional 4WD system may not be as efficient, but is both simple and reliable.
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Budd Stanley & Chrysler
Chryslers 4WD Systems
Active drive allows the Cherokee to be 2WD with the rear axle disconnected, or 4WD, able to send power to only two wheels with traction.
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Budd Stanley & Chrysler
Chryslers 4WD Systems
The Renegade's 4WD selection dial allows push-button transfer case operation and a dial to put the system in the ideal mode for the surface being driven on.
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Budd Stanley & Chrysler
Chryslers 4WD Systems
The rear differential of a Cherokee with the driveshaft disconnect.
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Budd Stanley & Chrysler
Chryslers 4WD Systems
The front two-speed transfer case and differential of a Cherokee.
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Budd Stanley & Chrysler
Chryslers 4WD Systems
Even the big Grand Cherokee can find traction in the most slippery of circumstances.
Story & photos by Budd Stanley, additional photos courtesy of Chrysler
What you need to know about Quadra-Trac, Active Drive and Rams 4WD drivetrains
Not so long ago the distinction between 4WD and AWD was rather simple. A 4WD drivetrain utilized a transfer case with two or more speeds that could be shifted from 2WD to 4WD when the occasion arises. AWD was a full-time single speed drivetrain that simply gave drivers piece of mind that power was being directed to at least one wheel both front and rear.
Today with the demands from both customers and governmental regulations to produce more fuel-efficient 4WD’s, the drivetrains of the modern 4WD have now become a complex mixture of computers mastering over their mechanical hardware slaves. The rapidly changing world of the 4WD is so cutting edge and at times complicated, even we need a quick training session to get down to the nuts and bolts of how modern drivetrains distribute power and save fuel.
For just this reason, Chrysler had us out to Quebec to drive all their different 4WD vehicles, allowing us to experience the characteristics of each system they employ. We also had a chance to talk to Mike Kirk, the head of Driveline Engineering at Chrysler to get the breakdown of each system. This is what we learned.
Ram 1500, Heavy Duty and Power Wagon
Lets start with the more traditional 4WD system that is found on the Ram pickups. This is your typical part-time 4WD drivetrain centred around a two-speed transfer case that offers three operating ranges: 2HI (two-wheel drive), 4HI (four-wheel drive) and 4LO (low-range reduction four-wheel drive) plus a neutral position. When equipped, an on-demand transfer case affords drivers the flexibility of an “Auto” setting that essentially mimics the characteristics of a full-time system, engaging 4WD when wheel slippage is detected.
The transfer case directs engine torque to both the front and rear differentials. In the case of the Ram Heavy Duty, electro-magnetic actuators mechanically lock both front and rear differentials. The Heavy Duty also has front axle disconnect system that allows front drivetrain components to be disconnected from the drive system to reduce parasitic loss and improve overall efficiency.
Jeep Wrangler
The Jeep Wrangler makes use of a similarly simple 4WD system found in the Ram’s, however it allows for three different final drive ratios in the Dana 30 front and Dana 44 rear axles. An optional Trac-Lok Limited Slip Differential (LSD) in the rear improves traction directing power to both rear wheels equally once one starts to slip.
The Wrangler Rubicon builds on this system by adding a Dana 44 front axle and electrically actuated, mechanical locking front and rear differentials. In this system, the driver manually engages the lockers rather than the automatic operation of the LSD.
Jeep Cherokee and Renegade
Jeeps latest inclusions to their lineup make use of one of the most forward thinking 4WD systems available today. These high production small CUV’s need to meet the demands of both soccer moms looking for a safe, fuel efficient, all-weather vehicle, and Jeeps own self designated “Trail Rated” abilities.
As such, the Cherokee and Renegade are driven by the Active Drive 4WD system that works like a proper 4x4 when in 4WD. When in 2WD, power is directed to the front wheels with the driveshaft disconnected from the rear differential, reducing energy loss and thereby improving fuel efficiency. The system comes in five different variants between the two vehicles, as follows:
Jeep Active Drive
Available in the Renegade, Jeep Active Drive is a fully automatic 4WD system that seamlessly shifts in and out of four-wheel drive at any speed once slip is detected. This system requires no driver intervention and delivers yaw correction during dynamic events. A fully variable wet clutch housed in the rear-drive module utilizes the Jeep brand’s proprietary controls to provide the proper amount of torque for any driving condition, including low-traction surfaces and dynamic off-road driving.
Jeep Active Drive I
Available on the Cherokee Sport, North and Limited models, Jeep Active Drive I is essentially the same as Active Drive, only mounted in the Cherokee. The system does not require any driver intervention or feedback, as a fully variable wet clutch housed in the rear drive module senses front wheel slip, engaging 4WD with a balanced torque distribution being sent to the rear wheels.
Jeep Active Drive II
Available on the Cherokee North and Limited models, Jeep Active Drive II includes a two-speed PTU (Power Takeoff Unit – fancy name for an intelligent centre differential) with torque management and low range. 4-Low mode locks the front and rear drive shafts for a 2.92:1 gear reduction to enhance the Cherokee’s climbing ability as well as improving the vehicles ability to crawl over severe off-road conditions.
Jeep Active Drive Lock
Available on the Cherokee Trailhawk, Jeep Active Drive Lock includes all the features of Jeep Active Drive II and adds an electronic locking rear differential for increased low-speed power for rock crawling or severe off-road conditions. The locking rear differential is selectable in any low-range terrain mode, but will lock automatically when in certain modes, such as “Rock,” to maximize tractive effort. The locker is controlled through the drivetrain and not the brakes, resulting in even brake wear over long-term usage.
Jeep Active Drive Low
Available on the Renegade Trailhawk, Jeep Active Drive Low is a two-speed PTU to the Jeep Active Drive system. This gives the Trailhawk 4-High and 4-Low, the latter yielding a 20:1 crawl ratio for challenging off-road conditions.
Jeep Grand Cherokee
The larger Grand Cherokee utilizes the slightly less sophisticated Quadra-Trac 4WD system that is RWD based in 2WD. This system is a full-time 4WD that is a mix of the more traditional Ram and Wrangler systems and the newer systems used by the Renegade and Cherokee, only without the ability to disconnect.
Jeep Quadra-Trac I
The Quadra-Trac I system is a single-speed transfer case that accommodates a full-time 4x4 system. The system requires no driver intervention, as there are no switches or levers to pull.
Jeep Quadra-Trac II
Quadra-Trac II adds a two-speed transfer case to the Quadra-Trac I system, allowing drivers to select 4WD high or low. When wheel slippage is detected, as much as 100 per cent of available torque is instantly routed to one or more axles with the most traction.
Quadra-Drive II
The Quadra-Drive II system adds Electronic Limited-Slip Differentials (ELSD) to the front and rear axles of the Quadra-Trac II drivetrain. This allows torque to be transferred both side-to-side and front to back through the use of the limited slip system.
Quadra-Trac SRT
Quadra-Trac SRT is an active full-time on-demand 4x4 system specifically setup to work with the 6.4L HEMI. The system features a massive mechanical “wet” clutch and ELSD in the rear, which allows 100% of the drive torque to be sent to one rear wheel. Management of torque split and suspension damping is accomplished with a dial on the five-mode Selec-Track system.