Jeep four-wheel-drive systems

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).

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.

From 1981 to 1988, a similar system was employed, dubbed "Select-Drive", which allowed the vehicle to switch from all wheel drive to 2WD using the NP129 model transfer case.

Overall, this system functions very much like the NP228 transfer case above, just with all of the mode and range controls via a single, console-mounted shift lever.

The transfer case has no center differential, so power can only be supplied to the front axle when the rear wheels begin to slip.

In 4WD Low mode, the clutch pack is locked and power flows through a 2.72:1 planetary gear set for higher torque at lower speeds.

It was a chain-drive system introduced in 1973 on the full-sized Jeep line behind the AMC version of the Turbo-Hydramatic 400 automatic transmission.

In 4H (full-time 4WD High) a center differential with a viscous limited-slip coupling is used between the front and rear output shafts.

The 'N' mode disengages the transfer case, transmission, and engine from the axles, thus enabling flat-towing the Jeep behind another vehicle.

Like the NP219, this transfer case utilizes a center differential with a viscous coupler to provide smooth and efficient four-wheel drive operation on all surfaces.

In normal 4WD All-time mode, the center differential is open and distributes torque to both the front and rear axles.

Applications: Quadra-Trac II was introduced in 1999 and it employs a two-speed chain-driven transfer case featuring three modes of operation, "4-All Time", "N" or neutral, and "4-Lo".

For the 1999-2004 Jeep Grand Cherokees using the NV247 transfer case, in "4-All Time" mode torque is applied to only the rear wheels under normal driving conditions.

A gerotor pump is connected between the front and rear output shafts and senses any speed difference between them.

When the shafts are turning at different speeds (wheel slippage), the pump supplies oil under pressure to a wet clutch pack.

There is no center differential, so on dry pavement the front and rear output shafts cannot be locked without causing driveline binding.

In "4-Lo" mode, the input shaft drives through a 2.72:1 reduction planetary gear set and the front and rear axles are locked together through the clutch pack.

This transfer case actually has a center differential, allowing both the front and rear axles to have power supplied to them without driveline binding, even on dry pavement.

There is also an electronically controlled variable lockup clutch pack that can apply progressive 0 to 100% locking across the center differential.

When it senses a left-to-right speed differences between wheel hubs BTCS can apply each of the vehicle's brakes independently, similar to anti-lock brakes, enabling Quadra-Trac II's open front and rear differentials to offer limited-slip capabilities.

Quadra-Drive uses the New Venture Gear NV247 transfer case mated to front and rear axles containing Jeep's Vari-Lok which are gerotor-equipped differentials.

Applications: Quadra-Drive II uses the New Venture Gear NV245 transfer case mated to front and rear axles containing electronic limited slip differentials or ELSDs.

Jeep added traction control in 2005 and starting in 2011 only a rear ELSD is offered, while the front has an open differential.

Trail Rated Jeep vehicles are determined by meeting several requirements of off-road conditions including water fording, articulation, and other tests.

Skid plates and tow hooks are options in the EU, but the hill descent control system is not available.

When in "4-Low" mode the front and rear axles are locked together and power is sent to all four-wheels through a 2.92:1 gear reduction in the power transfer unit; providing a crawl ratio of 56:1 for four cylinder Jeep Cherokees and a 47.8:1 crawl ratio for six-cylinder Cherokees.

[13] Applications: Selec-Terrain is a system designed to calibrate the vehicle to provide the best on-road and off-road performance; depending on which terrain mode is selected.

The modes are selected by a dial located near the center console and have five settings: "Auto", "Snow", "Sport", "Sand/Mud" and "Rock".