4wd explained
The first part of this article briefly talks about the difference between four-wheel-drive (4wd) and all-wheel-drive (AWD). The second part explains how and when to engage 4wd in your Jeep. If this text seems familiar, yes this is an excerpt from our Beginners Guide to Offroading.
4wd versus AWD
Not to alienate my fellow Subaru drivers (besides owning a Jeep Wrangler, we also have a Subie Outback Wilderness), there is a world of difference between 4wd and All Wheel Drive (AWD). I am not going to get into all the technical details here, though it is easy enough to Google should you want to explore the subject. In a nutshell, AWD translates into Any Wheel Drive.
Power goes to any of the four wheels, as needed. A differential determines if power should go to Driver or Passenger side; or if power should be directed from Rear axle to Front axle. Many of the “civilian” SUV’s that promote themselves as AWD could just as easily be considered one-wheel-drive! Subaru uses sophisticated computer control to achieve a more consistent power distribution that comes closer to 4wd than their competitors, but they still depend on differentials.
Differentials, by their nature, send the most power to the wheels or axles that have the least traction – which is counterintuitive to what we want to happen on a trail. Subaru is really good about correcting for that, which makes them such great cars. But in extreme terrain, the CV transmission and differential drivetrains just won’t supply enough power/torque to a wheel for the car to overcome the obstacles that a Jeep Wrangler or 4-Runner could easily manage.
Compare that to 4wd. A transfer case, not a differential, can lock both axles to the driveshaft so that 50% of the power always feeds front and rear. Differentials are still determining how much power goes to Driver and Passenger, but lockers or limited-slip-differentials mitigate that. Low gear transfer cases can generate even more direct torque to the wheels, providing the power to climb over rocks and ascend steep, slippery hills.
You can think of it in a layman’s way like this. Differentials suggest where power ought to be directed. Transfer cases and lockers demand where power is directed, and don’t take no for an answer!
Note that our article about Traction Control explains this in more detail.
Owning both a Jeep and a Subie, I can testify that there is a significant difference. The AWD performs better on wet highways and light snow than the Jeep, since the Jeep is generally in 2wd on paved roads; and the Subie does just fine on mild offroad trails. But even the forest rangers know that uncertain offroad conditions might stop an AWD and will post signs indicating that some roads are restricted to “4x4 High Clearance Vehicles Only”. They will ticket you if you are caught driving an AWD, even a respectable Subaru.
Understanding 4wd in your Jeep
What do Lockers do?
The Driver and Passenger wheels are locked together, and the differential no longer allows for slight speed differences between either side.
Normally, when any vehicle turns left or right, the outer wheels will spin faster than the inner wheels. The role of the differential is to allow this difference in turning rate on either side of the axle to avoid dragging the tire or binding.
When the differential is LOCKED, both wheels rotate in sync with each other, regardless of either wheel losing traction. Great on straightaways, but not good if you are turning.
You can engage lockers for the front, rear, or both axles.
Limited-slip rear differentials, which is an option on some Jeeps, are somewhat similar to a locker in that they try to maintain even power to both wheels, even if one tire loses traction. Not as good as a locker, but much better than a standard open differential.
Not all Jeeps come equipped with lockers or limited-slips. Rubicons feature Lockers for front and rear axles. We ordered our Sahara with the optional Limited-slip rear differential.
Transfer case shifting lever (which is separate from the transmission shifter)
The transfer case, unlike the differential found in AWD vehicles, directly engages (or disengages) the driveshaft with the front axle. 50% of the engine power is directed to both axles. There is no difference allowance for rotational speed (as there would be with a differential) when the transfer case is engaged. Both axles will rotate in sync at the same speed. The transfer case shifter allows you to choose between two gearing ratios: 4wd-Hi for more speed but less torque; or 4wd-Low for greater torque but slow speed.
2-Hi: This is your standard driving mode. Power is only applied to the rear axle. Always use 2-Hi when driving on dry, hard non-slippery surfaces such as asphalt, cement, or solidly baked offroad trails that feel like nature cemented over them.
When your dirt trail connects with a maintained road, remember to shift from 4wd back to 2wd until you return offroad.
4-Hi: This mode engages 4wd so that power is applied to front and rear axles equally. It is okay to drive in 4-Hi up to 50 mph.
You can freely shift between 2-Hi and 4-Hi on the fly, so long as you are under 50 mph. Just pull the lever straight back towards you (or push it forward away from you).
When your car is in motion, all four tires naturally rotate at separate speeds during a turn. On straightaways, your four tires are in step with each other; but when you turn, the front axle rotates at a different angle than the rear axle, which means it is at a different speed. Also, the inner tires rotate slower than the outer tires.
4wd wants both axles and both sides to be in sync, which does not happen while turning. So we don’t want to use 4wd on dry surfaces that would force our tires to skip or drag, while creating undesirable torque to our drivetrain.
Instead, we want to drive on loose, slippery roads that facilitate some tire slip & slide. Otherwise we are generating twist to the drivetrain components. Loose dirt or gravel, wet, muddy, or snowy paths are optimum for 4wd.
“If you encounter an obstacle, or need to control your downhill speed, learn how to use the semi-manual Sportsmode, sometimes called a Paddle Shifter. Pull the Transmission Shifter sideways towards the driver from D to M, and it will allow you to manually toggle (no clutch to worry about) between all your gears. M1 being the lowest, slowest, but most powerful —useful for steep hill ascents or descents. M2 or M3 if you want a little more speed. Pushing the lever forward will select the lower gear and pulling it backward will raise the gear. Judicious use of the low gears will prevent you from riding the brakes when coasting downhill.”
Although you could work your way through all of the available gears, I usually just nudge the Transmission Shifter back to the Drive (automatic) mode beyond M3 or M4.
4-Low: Use this mode for maximum torque to your wheels but try not to exceed 25 mph. Most of the time, we are in the 5-15 mph range. Low gear is for clambering over obstacles, tackling steep hills up or down, and places where you need strength & traction. For even better control during steep ascents/descents, use the semi-manual gearing such as M1 or M2.
There are many Trail Leaders who just remain in 4-Low the entire time they are offroad, but feel free to ask the Trail Leader to advise when you should be in 4wd Hi or shift to Low.
Shifting in and out of 4-Low can be tricky at first, especially in a Jeep. New Jeeps can be difficult to shift for the first few tries, until the gears wear in a little. Ask the dealership or a fellow Jeeper to teach you.
First, come to a complete stop, or at least a very slow crawl not more than 2-3 mph. Most of the drivers that I know prefer to stop completely.
Shift your Transmission from D to Neutral.
From 4-Hi, push the transfer case shifter sideways toward the Passenger, and then yank it towards the rear. The first pause puts it into Neutral. Pull hard some more until it clicks into 4-Low. The indicator in your dashboard will show what setting you are in.
Then, go back to the Transmission shifter and return it to Drive.
After several practices, this process will become second nature.
If the transfer shifter is stubborn and doesn’t want to go from Neutral down into 4-Low, try letting the Jeep roll a couple feet to facilitate the teeth in the Transfer case to realign.
If you are on a Trail run and either forgot how to shift between 4-Hi and 4-Low, or the Jeep is uncooperative – use your radio and ask someone to help you! Do not be embarrassed; mastering the art of the Jeep transfer case is a rite of passage that all of us have struggled with, and that the commercials never mentioned.
