FAQ & GLOSSARY

Full of questions but short on time? Take a deep breath — we've compiled a list of frequently asked questions so you can spend less time at your computer and more time on the trails.

What is the difference between Full-Time & Part-Time 4WD systems?
Full-time 4WD systems utilize a center differential, which enables the front and rear driveshafts to turn at different speeds, thereby allowing engagement on dry surfaces for normal driving conditions. A part-time system does not employ a center differential and locks the front and rear driveshafts together. With a part-time system, 2WD mode should be used during normal driving conditions and 4WD mode is to be used only when off-road or on wet or slippery surfaces.
Why can't you use Part-Time 4WD on dry surfaces?
Part-time 4WD systems effectively lock the front and rear driveshafts together, forming a single driving unit that does not allow for differential action between the front and rear driveshafts. Driveline noise and binding (Crow Hop) may occur when operated excessively on dry surfaces or in turns. This binding can lead to heat buildup and early part failure.
Why does "Crow Hop" occur?
When a vehicle turns, each wheel rotates on a different radius to the turning circle, thus traveling at different distances and speeds. If the vehicle's front and rear axles are locked together and are turning on dry surfaces, the difference in wheel speed sometimes results in driveline binding that is released with a "bang" or vehicle "shudder" when one of the tires loses traction.
Can I shift into 4WD High-Range at any speed?
Shifting into 4WD High-Range can be made with the vehicle stopped or in motion. If the vehicle is in motion, shifts can be made up to 55 mph (88 km/h).
How long can I drive in 4WD High-Range?
With a part-time system, prolonged driving in 4WD high-range is recommended only for wet, loose, or slippery road surfaces. With a full-time system, you need not worry about switching to 2WD mode when road surfaces improve.
How fast can I drive in 4WD High Range?
You should not go faster than road conditions permit.
What is 4WD Low-Range?
4WD low-range is a mode specifically designed for temporary use when additional traction and maximum pulling power is desired. Front and rear driveshafts are locked together and engine power is sent through another set of gears to multiply torque.
Avoid attempting to engage or disengage Low Range with the vehicle moving faster than 2 to 3 mph (3 to 5 km/h) and do not use this mode for normal driving.
Can I shift into 4WD Low-Range at any speed?
No. With the vehicle rolling at 2 to 3 mph (3 to 5 km/h), shift an automatic transmission to Neutral or depress the clutch pedal on a manual transmission. While the vehicle is coasting at to 3 mph (3 to 5 km/h), shift the transfer case lever firmly through Neutral and into the low-range position.
How fast can I drive in 4WD Low-Range?
Do not exceed 25 mph (40 km/h).
Can I shift into 4WD Low-Range when stopped?
Shifting into or out of 4WD low-range is possible with the vehicle completely stopped, however, difficulty may occur due to the teeth of the gears not being properly aligned. The preferred method to engage the low-range is to slow down to 2 to 3 mph (3 to 5 km/h) and put the transmission in Neutral. While still moving forward, move the shift lever firmly into the four-low position. Then return the transmission to the desired gear. Refer to your owner's manual for detailed instructions.
What if I never use the Selec-Terrain ® switch?
In AUTO mode, the vehicle will automatically select the correct drive system for the condition it senses.

Select a term to view its definition.

Approach Angle
Starting from level ground, this is the degree of slope a vehicle can approach without scraping or hitting the front undercarriage. It's a great indication of the ability to navigate severe off-road terrain like boulders and logs. A short front overhang produces high angles of approach, thus increasing off-road ability.
Articulation
A Trail Rated ® suspension is limber like a gymnast. How exactly? Flexibility is the key to good articulation. The more a wheel can travel, or flex, the better it can maintain contact with terra firma and provide the traction needed to cross an array of obstacles.
Axle Articulation
The ability of one axle to move relative to the chassis. It is the measure of the ease with which tires stay in contact with the ground (and retain traction) on very uneven terrain.
Axle Differential
An axle differential is a gear system located in the center housing of an axle assembly designed to allow the wheels to rotate at different speeds during cornering.
Axle
A rigid piece of metal that connects the front and/or rear wheels together. The suspension components attach to the axle and to the vehicle's body frame.
Brake Traction Control System
Transfers torque from one wheel to another on the same axle when wheel slip conditions are detected.
Breakover Angle
The degree of slope that defines the largest ramp or hill that a vehicle can travel over without scraping against the frame or underbody components.
Center Differential — Geared
A gear system located inside the transfer case of full-time 4WD vehicles. It is used to distribute drive torque to the front and rear driveshafts and allows the front and rear wheels to rotate at different speeds during cornering.
Clutch Plates
A series of alternating steel plates within the transfer case of many on-demand or automatic 4WD systems. One set of plates is splined to the clutch assembly hub of the rear driveshaft; the other set is splined to the clutch drum attached to the front driveshaft. The clutch housing is usually filled with a viscous, silicone-type fluid that clings to the discs to help transfer torque to the driveshaft. The engagement of clutch plates can also be controlled electronically.
Coil Springs
A coil of flexible metal that can be compressed or stretched along its centerline axis without permanent deformation. Coil springs support the weight of the vehicle while allowing the wheels to travel up and down over bumps.
Continuously Variable Transaxle
A stepless transmission that uses a sheave clutch to transmit engine torque.
Crawl Ratio
Essential for serious off-road treks involving steep hill climbs and descents, this is the final drive ratio of a vehicle in low-range. It allows Jeep ® vehicles to "creep" along (without depressing the accelerator) at very low speeds. Essentially, the vehicle does all the work. Crawl ratio is determined by this formula: first gear ratio x rear axle ratio x low-range 4WD ratio. The higher the number, the better the off-road capabilities.
Crow Hop
Vehicle shudder and tire scuffing due to a binding condition in the driveline. Usually caused by operating in basic 4WD or part-time 4WD modes on dry pavement.
Departure Angle
When returning to level ground from a descent, this angle indicates the degree of a slope from which a vehicle can depart without scraping or hitting the rear undercarriage.
Differential
A gear system that transmits torque to the drive wheels, while also allowing the wheels to rotate at different speeds when cornering. 4WD vehicles have differentials in both the front and rear axles.
Driveshaft
Shaft connecting the transmission output shaft to the differential drive pinion shaft. Four-wheel-drive vehicles add a second driveshaft from the transfer case to the front differential.
Electronically-Controlled Coupling
Manages the torque split from front to rear with no driver input needed for smooth and automatic performance.
Fixed Yoke Output Assembly
Effectively handles the extra output from the transfer case and helps to ensure smooth and durable driveline operation.
Four-Wheel Drive
A drivetrain that utilizes a transfer case to distribute engine power between the front and rear axles in order to drive all four wheels. Full-time four-wheel-drive systems utilize a center differential, which enables the front and rear driveshafts to turn at different speeds, thereby allowing engagement on dry pavement for normal driving conditions. A part-time system does not employ a center differential and, during normal driving conditions, must operate only in two-wheel drive. With a part-time system, the four-wheel-drive mode is to be used only when off-road or on wet or slippery surfaces.
Front Axle Disconnect
A mechanical or vacuum-operated component used primarily on four-wheel-drive models to connect and disconnect drive torque to the front axle. When shifting from four-wheel drive to two-wheel drive, this system disengages the front axle from the front driveline, so that the front wheels aren't turning the front driveline unnecessarily. This reduces unnecessary front driveline wear, noise and fuel consumption.
Ground Clearance
Don't drag your belly through the mud—just clear nasty logs, rocks, and uneven ground without sustaining undercarriage damage. Jeep ® Trail Rated ® 4x4s feature optimized approach, departure, and breakover angles to keep you in the clear.
High-Range
A 4WD mode used for on-road or light off-road use.
Hill Descent Control
This system uses the antilock brake system braking to control the car's motion downhill. Also allows a smooth and controlled hill descent in rough terrain without the driver needing to touch the brake pedal. If the vehicle accelerates without the driver input, the system will automatically apply the brakes to slow down to the desired vehicle speed.
Jounce/Rebound
The motion of a wheel that compresses its suspension. If a wheel is at full jounce, it is at the upper limits of its travel. The opposite of jounce is rebound — or wheel movement that decompresses a vehicle's suspension.
Limited-Slip Differential
Provides the same basic functions as an axle differential, but with an added advantage: when the drive wheel begins spinning as a result of being on a slippery surface, a limited-slip differential automatically transfers torque to the opposite wheel to help improve traction.
Locking Differential
Provides even more traction than a limited-slip differential by "locking" the axle shafts together when the driver wants to do it. Locking differentials do not allow for wheel speed differences and must not be used on dry, paved roads.
Low Crawl Speed
The "crawl ratio" is the lowest gear ratio in a vehicle and is determined by multiplying the first gear ratio by times the low-range ratio and the axle ratio.
Low-Range
A 4WD mode used for severe off-road conditions.
Maneuverability
Athletic. Agile. Trail Rated ® . Jeep ® 4x4s have the footwork to navigate narrow gaps, dodge emergency situations and avoid cosmetic damage to underbody sills thanks to precision steering and optimized wheelbases. Even gazelles don't move like this.
Neutral
When the shifter is in this position, the front and rear axles spin freely. Sometimes used for towing a Jeep ® vehicle behind another vehicle (such as a motor home), so that uncoupling the driveshafts is not required. Also used in the process of shifting into 4 Low.
Open-Center Differential
Located in the transfer case on some full-time four-wheel-drive vehicles, this component works in the same way as an open differential in the axles, but is of a more compact design. This component employs a planetary gearset, with planetary gears that revolve around the sun gear and inside the ring gear.
Power Robbing Friction
Surface resistance to relative motion, as of a body sliding or rolling.
Running Ground Clearance
The distance from the ground to the lowest point between the axles.
Shift-on-the-Fly
The ability to shift from two-wheel drive to four-wheel drive while the vehicle is moving.
Skid Plate
Helps protect the undercarriage from damage when driving off-road.
Solid Axle/Coil Springs
Ideal off-road equipment. Instead of each wheel on an axle being sprung separately (like independent suspension designs), a solid axle connects the suspension of two wheels. Coil springs then support the vehicle's weight and allow the wheels to travel up and down over terrain.
Suspension Travel
From full jounce to full rebound, this is the amount of vertical wheel movement allowed by the suspension.
Tow Hooks
Heavy-duty forged steel hooks in the front and rear of a vehicle that provide attachment points for snatch-em straps and winch cables (see the Off-Road Driving Tips section) should you get stuck.
Traction
Traction in 4x4 is equivalent to grip on Asphalt. Trail Rated ® traction helps you stay in control on untamed terrain, slippery (wet, mud, snow) conditions, and on steep grades.
Transfer Case
Mounted behind and driven by the vehicle transmission, the transfer case transmits power to the front and rear driveshafts in 4WD Jeep ® vehicles and offers high and low range. For the full line of Jeep transfer cases see the Get Ready section.
Transmission
A mechanism that transfers torque into usable driving power through the use of gear sets. These gear sets multiply engine torque in varying amounts to meet specific driving demands.
Two-Wheel Drive
When the shifter is in this position, the front axle spins freely while power is sent to the rear axle and wheels, which then drive the vehicle.
Viscous Coupling
A speed-sensitive device located in the transfer case that transmits drive torque between the front and rear driveshafts when wheel slip occurs. Viscous couplings are typically used on all-wheel-drive vehicles and vehicles with automatic and on-demand four-wheel-drive systems.
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