4WD and AWD Systems Explained for Current FCA US Vehicles

Jeep Wrangler 1 photo
Photo: Catalin Garmacea
From the 2015 Chrysler 200 mid-size sedan to the 2015 Jeep Wrangler off-road all-star, Fiat-Chrysler Automobiles' North American arm is currently employing lots of 4WD and all-wheel drive drivelines. This simple guide aims to explain how these systems differ from one another and what FCA US LLC vehicles come or can be optionally equipped with them.
FCA describes itself as a "global leader in axle-disconnect and active-transfer-case technologies," but how does that translate for every customer desire and operating condition? Thankfully for the curious out there, here's a quick rundown of FCA's systems:

RWD-based 4x4 systems

With this type of driveline, Fiat-Chrysler can squeeze the most off-road capability out of its current line of vehicles. Starting with the 2015 Jeep Wrangler, this model benefits from a system that employes live axles and electronic lockers for a lot of capability off the beaten path.

Built on seven decades of 4x4 engineering experience, the Wrangler is available with 3.21, 3.73 or 4.10 ratios depending on the model. A Dana 30 front axle and a Dana 44 rear axle are employed by the Sport and Sahara models. Additionally, the Command-Trac NV241 part-time two-speed transfer case features a 2.72:1 low-range gear ratio, while the optional Trac-Lok limited-slip rear diff is there to provide extra torque and grip when the going gets very rough.

The 2015 Jeep Wrangler Rubicon, on the other hand, gets two heavy-duty Dana 44 axles and the Rock-Trac NV241 two-speed transfer case with a 4.0:1 low-range gear ratio. The Rubicon is also equipped with electric front and rear locking diffs, as well as a disconnecting front sway bar for unrivaled off-road capability.

In comparison to the Wrangler, the Jeep Grand Cherokee can be had with three full-time 4x4 systems, all of them RWD-based: Quadra-Trac I, Quadra-Trac II and Quadra-Drive II. The Quadra-Trac I system features a single-speed transfer case that accommodates full-time 4x4.

The Quadra-Trac II’s two-speed transfer case uses input from a variety of sensors to determine tire slip. When wheel slippage is detected, as much as 100 percent of available torque is instantly routed to the axle with the most traction. The system can be enhanced with an electronic limited-slip differential as well.

The last family of models that use RWD-based 4x4 systems is the 2015 Ram 1500 4x4 and the 2015 Ram Power Wagon heavy-duty workhorse. Frankly speaking, a rear wheel drive-based four-by-four system is mandatory on pickup trucks designed to tow and haul extremely heavy loads.

FWD-based 4x4 systems

FCA US also does FWD-based 4x4, as seen on the Jeep Cherokee. Speaking of this model, did you know that the Cherokee is the first mid-size SUV to feature rear-axle disconnect for better fuel economy? This system can switch from 2WD to 4WD for full-time torque management and doesn't require driver input.

Available on the Sport, Latitude and Limited models of the Cherokee, the Jeep Active Drive I system features a single power transfer unit (PTU), which is fully automatic. Therefore, it delivers seamless operation in and out of four-wheel drive at any speed, without requiring any driver intervention.

The Jeep Active Drive I 4WD uses a fully variable wet clutch housed in the rear drive module. As for the Jeep Active Drive II (available on all three of the aforementioned models), this includes a two-speed PTU with torque management and low range. The system's 4-Low mode locks the front and rear drive shafts for low speed power or towing, while low range provides a 2.92:1 gear reduction for better climbing ability and crawl in off-road conditions.

Jeep Active Drive Lock is the most advanced front wheel-drive-based 4x4 system currently available for the Cherokee mid-size SUV. What it adds over the Active Drive II is a locking rear differential for better capability and that's about it.

RWD-based AWD systems

This type of driveline is available for the 2015 Dodge Charger, 2015 Chrysler 300 and the 2015 Dodge Durango. Starting with the Durango, customers are offered with a full-time AWD system that uses three separate open diffs: one in its transfer case and one in each of its axles. In addition to this, the Durango's AWD system gets a low-range transfer case with a neutral position that improves light off-road performance.

In the 2015 Dodge Charger's and Chrysler 300's case, the AWD system integrates an active transfer-case and a front-axle-disconnect feature to enhance two things first and foremost: handling and fuel efficiency.

The electronically controlled coupling (ECC) is at the heart of the system’s capability. In contrast, viscous-coupling systems require some degree of front-to-rear slip before torque is transferred to the rear wheels.

FWD-based AWD systems

With the 2015 Chrysler 200, the FCA Group showed the world that it's possible to make a mid-size luxury sedan with a rear-axle disconnect feature to improve fuel efficiency. The AWD system can disconnect and reconnect the rear axle as needed and at any speed, accounting for a parasitic loss reduction of up to 80 percent compared with other part-time AWD technologies.

In the 200's case, the transfer unit (PTU) and the rear-drive module (RDM) are the key elements of the system. Regarding the parasitic loss, some components are kept stationary when the vehicle is in front-wheel drive, elements such as the planetary gear sets and input clutch plates.

When AWD is engaged, up to 60 percent of the available torque can be transferred to the rear wheels.
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About the author: Mircea Panait
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After a 1:43 scale model of a Ferrari 250 GTO sparked Mircea's interest for cars when he was a kid, an early internship at Top Gear sealed his career path. He's most interested in muscle cars and American trucks, but he takes a passing interest in quirky kei cars as well.
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