Mk 1 discovery stuck in 4wd. Can select high and low ratio but when taken out of 4wd vehicle revs in gear no traction

The Borg Warner (BW) model 4493/4494 NR4 transfer case is a 2-speed, full-time 4WD, transfer case. The transfer case has an external planetary type differential, which has 2 different sets of pinion gears. The planetary differential provides a 40/60 torque split front/rear full-time. This means the front and rear propeller shafts are constantly being driven for maximum traction in all conditions. A high/low planetary carrier assembly provides the high and low ranges, which is a 6-pinion gear, sun gear, and annulus gear arrangement, giving a 2.64 low range reduction ratio in the BW 4493 and a 4:1 ratio in the BW 4494.

that vehicle came with a ratio changer before the main transmission on a separate lever
what you say indicates that it is in low range which makes the main transmission gears all low ratio gears
a good operator can by manipulation of the 2 levers actually get 10 gears ending up with high range overdrive or 5th gear
The top speed is around the 80 mph mark (120kph)
you could have the diff fitted with a new crown wheel and pinion to a lower ratio for more speed but you will sacrifice economy and take of on hills under load capability

you can switch into and out of the auto or 4 high modes while moving.

If you want to use 4 low you must stop and place your transmission in neutral. While stopped, turn the switch to 4 low. To get out of 4 low, again stop and in neutral switch back to desired mode. DO NOT SWITCH TO 4 LOW WHILE MOVING!

all wheel drive vehicles have to work at both ends all the time unless you have a major failure in the drive train. That is why it is called all wheel drive as opposed to 4 wheel drive. With 4 wheel drive you have the option of rear wheel drive or 4 wheel drive and normally in a high ratio or low ratio gear selection. With some all wheel drive vehicles there is a selector that locks the middle diff and creates a 4 wheel drive option without the high/low gear ratio option. So in practice if the both front wheels are in the bog then there is no all wheel drive as the centre diff is working as it should and placing all the action in the rear wheels which will not be turning as they have traction so the front wheels spin faster.. If you have a centre diff lock option ensure that it is operational.

Your JEEP is only part time 4WHEEL DRIVE as you can't DRIVE on the STREET with it, its NORMAL and nothing is WRONG.


Part-Time and Full-Time 4x4 systems...

A part-time 4x4 system called Commandtrac is in all Wranglers together with low-end Cherokees and Liberties. A part-time 4x4 system locks the front and rear driveshafts together inside the transfer case so they drive the front and rear axles together in lock step. Because they are locked together, the front and rear tires must rotate at the exact same rpms. However, the front tires must rotate faster than the rear tires during any turn so a part-time system fights that... which makes a part-time system inappropriate on a paved road because the high level of traction on a paved road prevents the tires from slipping which would otherwise allow the front and rear tires to grudgingly rotate at different rpms. Offroad this is not a problem since the poor traction of an offroad trail allows the tires to slip as needed. But when they try to slip/rotate at different rpms on a high-traction surface, the entire drivetrain is stressed which is bad for it. This problem is called "wind-up".

In reality however, the front and rear axles really don't even turn exactly the same RPMs when you're in 4wd so you still get "wind-up" if you drove in 4wd on the street even if you drove in a perfectly straight line. Why? Because 1) you can't drive in a perfectly straight line and 2) the front and rear axle ratios are usually .01 different from each other. Like a 3.73 and 3.74, 4.10/4.11, etc.. Why the .01 ratio difference between the front and rear axles? Because the front and rear axles usually have different ring gear diameters which makes it nearly impossible for the gear manufacturers to economically make the front and rear axle ratios exactly the same. And no, they are not made .01 different on purpose to make the front or rear pull more when in 4wd, that is an old wive's tale.

Finally, a full-time 4x4 system like Selectrac is available on Grand Cherokees, Cherokees and Libertys couples the front and rear axles together, but they are not mechanically locked together like they are with a part-time 4wd system. The front-to-rear axle coupling can be done via either a differential like the Selectrac system uses (just just like what is in the center of an "open" axle) or a fluid (viscous) coupler. The benefit to a full-time 4wd system is that because the front and rear axles are not mechanically locked together, the front and rear tires/axles can rotate at different rpms from each other. This allows a vehicle with a full-time 4wd system to drive in 4wd "full time" on a paved road without problem since there is no 'wind-up' problem to harm the drivetrain. You cannot get a full-time 4x4 system in a Wrangler from the factory.



HOPE THIS HELPS.

Hi Ralph.

I do not own a Durango, but have owned many 4WD vehicles and can offer tips for proper usage.

The "L" and "H" after the 4 and 2 stand for "Low" and "High" ranges. The 2 and 4 stand for the number of wheels that can receive power from the engine and transmission. Most 4WD vehicles only provide power to 1 wheel on each axle (front at rear for a total of just 2 wheels powered) at any given time (but for purposes of discussion, we'll call it 2WD & 4WD, as advertised).

Generally, "2WD" is only offered as a High range and is the same as a "normal" 2WD car or truck. I haven't seen a car or small truck that offers 2L (but I haven't seen a Durango - so I don't know), but generally 2WD traction can be increased easily enough by simply shifting the transmission to a lower gear (From "D" to "2" or "2" to "1", etc.).

4WD is designed to provide additional traction whenever 2WD isn't sufficient. This can be when surfaces are slippery such as sand, mud, snow and ice or, when pulling a heavy load such as a trailer and tires are not gripping the surface well. Shifting from 2WD to 4WD High will provide more traction at the same tire speed. Maximum power from the engine does not come at low RPMs, so in order to get more pulling power from the engine with out increasing speed (or spinning tires), the transmission should shifted into a lower gear. This is especially helpful when pulling a trailer up a wet incline, etc. If 4WD High in 1st gear is still allowing tires to spin or not providing enough pulling power, then shifting the transfer case from 4WD High to 4WD Low will allow the engine speed to increase (providing more power) without increasing the speed of the wheels (reducing the chances of spinning tires).

4WD should never be used while operating on dry pavement. Since tires wear at different rates, and turning left or right slows the inside tire and speeds up the outside tire when compared to the rear tires, a certain amount of slip is required. Wet surfaces provide this necessary amount of slip - as does sand, mud, snow, ice, dirt, gravel, etc. You should take the time to see how each selection of High and Low affects engine speed and vehicle speed and how the surface and any trailer further changes traction. With a little experimentation, you'll see how it works and be able to choose the right range with little thought.

Don't forget to have the transfer case & front differential fluids checked and changed as per the manual. Neglecting this simple service intervals can leave you stranded when you need 4WD and can be very expensive to repair.

I hope this helps & good luck!

The discovery is full time 4wd, you can change between high and low ratio, it sounds like a broken transfer case.

You can shift on the fly...as you are moving....into 4WD at speeds up to 40 MPH but simply grabing the 4WD selector and moving into the 4WD high gear. Low gear selection should be done at a stand still, with transmission in neutral position before proceeding in fwd. The low position is a "granny gear" that is for extreme situations where high 4WD will not suffice or get you out of a stuck situation.

Have you checked the High-Low ratio lever.  Half-way between High and Low is a Neutral, so no drive to any axle even if a gear in the main box is selected.
Try locking the differential.  If this gives you drive, then it might be a final drive (half-shaft) failure.

Let common sense be your guide. 4HI puts power to the front and rear wheels at the same ratio as in 2wd for gear selected, allowing for better traction at higher speeds. 4LO puts power to the wheels at a ratio for more torque to the wheels.Just remember that all 4 tires are pulling so handling may be alittle different.