Jeep uses a variety of four-wheel drive and all-wheel drive systems on their various vehicles. These range from basic part-time systems that require the driver to move a control lever to send power to four wheels, to permanent four-wheel systems that monitor and sense traction needs at all four wheels automatically under all conditions.
The makers of Jeep transfer cases are include Dana, Borg-Warner, as well as either New Process (NP) or New Venture Gear (NV) as indicated by the model numbers.
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The Dana 18 part-time gear system.[1] It uses a cast iron case and both the front and rear output shafts are offset towards the passenger side of the vehicle. Drive modes offered include 2-wheel High, Part-time 4-wheel High, and Part-time 4-wheel Low.
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The Dana 20 part-time gear system.[1] It is similar to the Dana 18 except that the rear output shaft is centered. This enables 2-wheel High to be direct-drive, which is quieter. Otherwise the Dana 20 offers the same drive modes as the Dana 18.
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The Dana 21 part-time gear system with single-speed case with automatic transmission.[2] The Dana 21 is essentially a Dana 20 without a Low range (only 2-wheel High and Part-time 4-wheel High).
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The Dana 300 part-time gear system.[1]
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Command-Trac was first introduced using the NP208 transfer case in the full-size Jeeps (SJ series) in 1980. The drive modes are the same as with the Dana 18 and 20 transfer cases: 2Hi, 4HI PT, and 4LO PT. The 4WD modes are not for use on high-traction surfaces such as dry roads. The NP208 was used through at least 1987.
More commonly, Command-Trac is used to refer to the NP/NV-231 or NP-207 transfer cases introduced along with the Jeep Cherokee (XJ) in 1984. The system offers a chain-driven, aluminum, "shift-on-the-fly" transfer case. The "shift-on-the-fly" feature provides manual ease and assist while engaging 4WD. Command-Trac should only be driven in 4WD on low-traction surfaces due to the front and rear axles being locked together (no differential action in the transfer case). Driving in 4WD on dry pavement causes excessive wheel and drivetrain wear. Four-wheel modes are most commonly used for wet/slick surfaces or extreme weather conditions (rain, snow, etc.) (4H), towing (N), and off-road activities (4L).
There are reports of a modified version known as NP-231J HD which was supposedly (SP) a "heavy duty" version for the Jeep Grand Cherokee ZJ with V8 engines. The NP/NV-231 case is a chain-driven unit that takes 21- or 23-spline input shafts. The 23-spline was for the AX-15 transmission, and the 21-spline was used for the AX-5 and BA 10/5 transmissions. Low range for this case was 2.72 and high range was 1.00.
The Command-Trac HD transfer case was used in 6-speed Liberty KJ's from 2005–2007. Although sometimes referred to as the "NV(NP)231HD," the transfer cases are actually the 241 series used in full-sized trucks from other makers (241D or 241C). The Jeep version is labelled "NV(NP)241J." This is not the NV241OR transfer case found in the Jeep Wrangler Rubicon, which uses a 4.0 low range and has a reinforced case. Dodge uses a 241DHD, which has a reinforced case but the 2.72 low-range.
The Jeep Grand Cherokee/Commander line no longer offers a part-time transfer case option. The reason behind this was its poor sales along with an improved Selec-Trac. Selec-Trac and a simplistic Quadra-Trac had the convenience and comfort of "Full-Time" all wheel drive that Command-Trac lacked for "luxury" SUV's that did not require the more rugged part-time system.
The terms "Command-Trac" and "Selec-Trac" where used in other Jeep lines and refer to different transfer cases in those lines.
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Selec-Trac was introduced in the full-size Jeeps in 1983 using the NP229 transfer case. The NP229 offered three modes: 2Hi, 4Hi full-time using a viscous-type limited-slip coupling, and 4Lo Locked. It was used from 1983 to 1991 in some applications.
The NP228 Selec-Trac transfer case is closely related to the NP229. The only difference is that the NP228 does not have limited-slip when in 4Hi full-time. It was used briefly in 1986.
The NP242 Selec-Trac transfer case debuted with the compact Jeep Cherokee in 1984, borrowed from the AMC Eagle. It is a more common feature in the upscale version Jeep Wagoneer (XJ), and Dodge Durango models (1998-present). It has a shift-on-the-fly transfer-case like Command-Trac but unlike it, Selec-Trac offers full-time all wheel drive in addition to the part-time 4WD of Command-Trac. Full-Time all wheel drive has the ability for the front and rear axles to rotate at different speeds, making driving on dry and wet surfaces possible year-round without shifting back to 2WD again. It still has the ability to lock the front and rear axles.
Other Jeep vehicles used Selec-Trac, for example, the Jeep Grand Cherokee, before being discontinued on that platform in favor of the electronically controlled Quadra-Drive II AWD system in 2005. Selec-Trac is currently only available for the Jeep Liberty lineup.
Selec-Trac uses the New Venture Gear NV242 transfer case[3] (formerly known as NP242).
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The Quadra-Trac name is used on a variety of full-time 4WD systems. The first version was launched in 1973, the Borg-Warner BW 1339.[2] An unrelated system was used in the 1980s. Yet another system carried the name in the 1990s.
Quadra-Trac was the trade name for the Borg-Warner 1305 and 1339 gear case. It was a chain-drive system introduced in 1973 on the full-sized Jeep line which included the Wagoneer, Cherokee, and trucks behind the AMC-specific Turbo-Hydramatic 400 automatic transmission. CJ7s also received the Quadra-trac. This system included a differential to shift torque between front and rear which could be locked with vacuum. The 1305 lacked a low-range, while the 1339 offered an optional 2.57 planetary gear. A Quadratrac transfer case can be upgraded from a non low range equipped unit to having low range by swapping in the optional planetary housing and shift rod and floor shifter assembly from another transfer case. Consult a factory service manual for service procedures.
The Borg-Warner 1305 offered only 4WD Hi modes in full-time or part-time (locked) modes. With the low range the BW 1339 offered four modes: 4HI FT, 4HIPT, 4LO FT, and 4LO PT.
The NP219 Quadratrac transfer case was used in full-size Jeeps from 1980 through 1982. It offered the following modes: 4HiFT, 4HiPT, and 4LoPT. In full-time 4WD High a viscous-type limited-slip coupling is used between the front and rear output shafts.
The Jeep Quadra-Trac was differentiated from the open "New Process" Gear NP203 used by Dodge, General Motors, and Ford in that it included a center limited slip differential feature, in this case a clutch pack.
The part-time case available in these vehicle at this time was the Dana 20.
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The Borg-Warner system was replaced with a "New Process Gear" NP219-based chain-driven system in 1980[4]
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The NP229-based system "New Process Gear" was replaced with a New Venture Gear NV249-based chain-driven system in 1996.
The NP249/NV249 utilizes a "Viscous Coupler" to determine power transfer between the front and rear axles. The goal of this device is to provide smooth and efficient 4WD operation on dry surfaces — if a differential in speed occurs between the axles, heat buildup in the viscous coupler transfers power to the slower axle, providing some traction in off road conditions. Splitting the torque to the front and rear, it is similar to several passenger car systems, but with a low-range gear for serious off-roading.[5]
1993-1995 NP249 transfer cases used the viscous coupler to transfer power in both high and low ranges.
1996-1998 NV249 transfer cases had a low-lock capability, meaning a hard gear transferred power in 4LO (front and rear drive shafts are locked at same speed in low range).
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Quadra-Drive employed the New Venture Gear NV247 transfer case. This two-speed chain-driven transfer case uses a gerotor, a clutch pack coupled to a hydraulic pump, to transfer torque between the front and rear axles. The transfer case contains three modes, 4-All Time, Neutral, and 4-Lo. In 4-All Time, torque is applied to the rear wheels under normal driving conditions. If the rear axle starts spinning at a higher rate than the front axle, hydraulic pressure builds up in the gerotor and causes the clutch pack to progressively transfer torque to the front axle until both axles return to the same speed. Neutral mode is intended for towing the vehicle. In 4-Lo, the front and rear axles are locked together through a 2.72 reduction gear ratio.
In Quadra-Drive, the NV247 transfer case is mated to front and rear axles containing Jeep's Vari-Lok differentials. Vari-Lok differentials also use a gerotor to transfer torque between the two wheels.
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Quadra-Trac II also employed the NV247 transfer case but lacked Quadra-Drive's front and rear Vari-Lok differentials.[3]
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Quadra-Trac I consisted of the New Venture Gear NV147 transfer case, a version of the NV247 transfer case lacking neutral and low-range modes.[3]
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Quadra-Drive II consists of the New Venture Gear NV245 transfer case mated to front and rear electronic limited slip differential. It includes a Neutral mode and utilizes a 2.72 reduction gear ratio in low-range.
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Quadra-Trac II consists of the New Venture Gear NV245 transfer case without Quadra-Drive's ELSDs.
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Quadra-Trac I consists of the NV1240 transfer case, a version of the NV245 transfer case lacking neutral and low-range modes.
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ALL 4WD systems in the WK come coupled with Jeep's brake traction control system (BTCS).
Freedom Drive is Jeep's four wheel drive system used in its compact crossover SUVs based on a front wheel drive platform, the Compass and Patriot. There are two versions of the basic Freedom Drive system for the US Market, called I and II.
Freedom Drive I is a light duty full-time electronically controlled all wheel drive system with a locking mode to set the front/rear torque split for especially slippery conditions in the Jeeps derived from the Chrysler/Mitsubishi GS Platform.
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Freedom Drive II uses the same hardware as the FDI system but adds a continuously variable transmission to simulate the benefits of a 19:1 low-range transfer case for off-road use. This function is an alternate program in the CVT and is not a transfer case function. FDII also adds hill descent control system, off-road tuned traction control, and electronic stability program. The Patriot with FDII also feature longer suspension travel, skid plates, tow hooks, and a full-size spare tire. This enables the FDII-equipped Patriot to wear the "Trail Rated" badge from Jeep. Trail Rated Jeep vehicles are determined by meeting several requirements of off-road conditions including water fording, articulation, and other tests.
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For the European Market there is a single version which combines elements of both U.S. versions. The European version is available with either a CVT gearbox or most commonly with a 6-speed manual gearbox and has two settings on the traction control and electronic stability program systems to cater for off-road activity, U.S. FDII suspension travel and a full-size spare tire. Skid plates and tow hooks are options in the EU, but the hill descent control system is not available.
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