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4WD, AWD, and Transfer Case Information and Operation

ExplorerDMB

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With winter weather somewhat over and ice/snow not much of a factor anymore - I thought I'd share some things for the common 4x4 "light use" enthusiast. Much of the service shops see at winter time is of coarse the four-wheel drive system. Many people have conerning questions about driveline noises or vibrations, especially on semi-iced roads. The popping and jerking while turning was of great concern. Some had difficulty disengaging the 4wd once the ice melted. A lot of repairs resulted from the vehicle finally receiving an inspection. Here are some of the greatest complaints.

The system that generates the majority of complaints is the part-time four-wheel drive system. The system ha scertain operational characteristics that can result in the inexperienced operator assuming that there is a problem within the system. On a part-time system, the transfer case splits the power to the front and rear axles. The transfer case allows the operator to select from rangers 2W/Hi, 4W/Hi, and 4W/Low. It is common for the gears to grind when shifting from neutral into one of the range selections. On this system, the front and rear propeller shafts turn at the same speed with no internal means of matching the tires' rotational rates from front to rear. The result can be driveline loading and increased noise conditions.

NORMAL OPERATIONAL CHARACTERISTICS
1) It is normal for the T-case to emit a noise when being locked into 4x4 engagement.
2) This system is designed for use on a low traction surface such as snow, ice, mud, dirt, etc. These types of surfaces allow for wheel slippage, preventing transfer case and driveline loading and binding (i.e. driving on dry pavement).
3) With 4x4 engagement, a popping and binding sensation should be considered normal when turning. During a turn, the front and rear axles follow a different arc. The compensate the tires must slip. The symptoms are referred to as a crow-hop or grabbing sensation. The same symptoms can occur when the tire circumference varies from front to rear. This is why it is imperative that the tires be rotated on a scheduled basis. Unequal tire pressure from front to rear can promote rotational variations.
4) The noise generated during 4x4 engagement should be considered a normal occurance, as more parts are turning. The noise level is greater when the vehicle is operated on a dry surface as opposed to a low traction surface and the noise level will be greater when driving in 4W/Low.

T-CASE DISENGAGEMENT
On a 4x4 system, especially those equipped with eletric shift (like 2nd-3rd Gens), the system may not disengage when the vehicle has been driven on a dry surface. The variation in the rates of tire rotation results in transfer case loading and binding. When this occurs, the pressure is too great for the electric shift motor to overcome. To confirm, place the vehicle on a lift, allowing the wheels to rotate freely. This relieves the pressure on the transfer case. If the transfer case will now shift properly, it confirms transfer case loading. The first check should involved a tire circumfrence measurement from front to rear. Often we encounter this condition folllowing the installation of the spare tire

TIRE CHECKS
1) Compare tire sizes from front to rear
2) Are all tires the same brand? Tire sizes vary from one tire manufacturer to another. (i.e. BFG 33" M/Ts = 32.6", Interco 33" SSR = 33.4")
3) Pressure check. A low tire has a different rotational rate than an inflated tire.
4) Measure the tread depth of all four tires, as they must be nearly equal.
5) Do not mix tread types, as rotational rates may vary.

AWD POWER TRANSFER UNIT FAILURE
Normally we associate an All Wheel Drive (AWD) system as one that is inteded for use in inclement weather and will operate smoothly on dry pavement. The system is usually designed to allow for a difference in front-to-rear axle rotations. Chrysler acknowledges an extremely high failure rate of their Power Transfer Units (PTU) used in 96-2001 AWD Town & Country, Caravan and Voyager vehicles. Chrysler said it was a design flaw, but later determined that the failures were due to lack of poper tire rotation. Failure to rotate the tires results in uneven front-to-rear tire wear. The variation in the tire circumference from front to rear results in an extreme heat build-up in the PTU. The condition occurs as a result of the continuous variation in rotational speeds and torque transfer between the front and rear drive components. A tire circumference variation as minimal as 0.5% can overhead the PTU. Chrysler recommends a tire rotation at 7,500 miles or less. Watch the air pressure from front to rear, as it can promote the same. When a tire replacement is necessary, chrysler recommends replacing all four tires with a matched set from the same manufacturer. At a cost of $1,200 for a PTU, a little tire maitenance makes good sense.



This isn't really a huge thing on how to fix things, but it's a way to keep from future problems and to possibly diagnois 4x4 problems yourself.

-Drew
 


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gijoecam

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Like I said before the General Explorations was closed, this is a nice article, but very little of it applies to the 2nd and 3rd generation Explorers. I would like to go through and write something up specific to the Explorers, but it would take a lot of time... maybe one day when it's extremely slow around here I can get to it with some pics and diagrams.

I'd love to, just don't have the time at the moment.

-Joe
 




ExplorerDMB

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I hope you do, Joe. This is basically an article to give people an idea of how things works and what can happen.

-Drew
 




bigbandit

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Just read your info on disengaging the transfer case. I am in the U.K and have a standard '94 XLT with electronic shift. After trying four wheel drive it is now stuck in 4 wd. I can hear the shift module in the back making a noise but it won't shift back into 2wd. If I jack all 4 wheels up off the groud and try to shift will this have the same effect as a lift. Please help. Thanks.
 




ExplorerDMB

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Yes, but spend the wheels by hand first and then try and disengage the 4wd. Now, this isn't the safest way, but it'll work. Just take precautions.

-Drew
 








bigbandit

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I've tried lifting all 4 wheels clear of the ground and spinning them. Then trying to shift back into 2wd, but it is still in 4wd and in low range. Any other suggestions.
-Kev. :(
 




ExplorerDMB

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That is odd. Is the shift motor doing anything? I wonder if that is frozen up?

-Drew
 




bigbandit

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Hi Drew, When pressing the button's for 4wd and low range there is a slight clicking noise from the shift motor, but the light's for the switch's for 4wd and low range are not coming on. It has been below freezing here for the past couple of day's and not much above it now. Thanks Kev.
 




Glacier991

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Stickied for the time being.
 




scheki

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Has anyone experienced there AWD to be locked on?
Just wondering what i am hearing in the front end, or wonder if it could happen. Thanks
 




ExplorerDMB

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locked on? What kind of noise are you hearing?

-Drew
 








BrooklynBay

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I saw a link with additional information on AWD, 4WD, RWD, and FWD. Here it is: http://autos.aol.com/article?id=20051228122609990001. Here is the article:
Updated:2005-12-28 12:27:53
What Drives You
FWD vs. RWD vs. 4WD: What are the differences?
By ERIC PETERS
Many people think a four-wheel-drive truck or SUV is the best way to get around in the snow. Not necessarily -- at least, not for most people, anyhow. A front-drive car with good winter tires may be a better choice. Or one equipped with all-wheel-drive.

Here are some of the pros and cons of each:

Four-wheel drive (4x4)
This system is typically found only in pickup trucks and truck-based SUVs. Typically, the system operates "part-time" -- with engine power going only to the rear wheels until the driver (or, in the case of automatic systems, the onboard computer) engages the front axles. Typically, the power split front-to-rear is not adjustable; that is, when in 4x4 mode, the front wheels get 50 percent of the engine's output and the rear wheels get the other 50 percent. Four-wheel-drive systems are also distinguished by the presence of a two-speed transfer case and 4x4 Low-range gearing.

The upside: 4x4 systems are great for off-road driving and muddy, uneven terrain; the 4x4 Low-range gearing makes it possible to crawl up steep inclines and slog through deep snow. These systems are designed to be very tough and can take a lot of abuse. They are great -- even essential -- for people who live in very rural areas or who must deal with heavy snow on unplowed country roads.

The downside: 4x4 systems usually operate in 2WD mode -- with just the back wheels receiving engine power. When in 2WD mode, these vehicles often have less grip than a FWD car. In addition, 4x4 systems are not optimized for use on smooth surfaces -- in other words, for most types of on-road driving. Excess wear and tear can occur if the system is put into 4x4 mode on dry (or wet) paved roads. These 4x4 systems are also not designed for high-speed operation, so operating the vehicle at highway speeds with the 4x4 engaged is not a good idea. Not many people understand these limitations -- even though the information is usually right there in the owner's manual. Finally, a 4x4 system adds considerable weight (and inertial load) to the vehicle, which in turn can cut down on fuel economy. While you may only need to engage the 4x4 a few days out of the year, you'll be paying for it every day by lugging around a couple hundred pounds of additional dead weight.

The lowdown: Buy a 4x4 if you need a vehicle with serious off-road capability or have to travel on rural (and unpaved) gravel or dirt roads -- or if you live in an area subject to severe winters where it's routine to have to drive through heavy snow on unplowed roads. Otherwise, it's a money waster.

Front-wheel drive (FWD)
Most passenger cars built today are front-wheel-drive -- as well as most minivans and so-called "crossover" vehicles that may look sort of like SUVs but are actually built on a car-based chassis.

The upside: FWD cars can actually be pretty tenacious in the snow because the weight of the engine/transaxle is sitting right on top of the drive wheels. FWD is vastly better in the snow than a rear-drive car -- and with the right tires, you will probably be able to make it to work unless the snow is really deep (in which case it's the absence of ground clearance more than anything else that will cause you to get stuck). FWD is also more economical -- both to buy "up-front" and to operate over the life of the vehicle. You're not paying extra when you buy the car -- and you're not paying every time you gas up to lug around equipment you only use a handful of times every year.

The downside: FWD cars are weight-biased toward the front, which is a built-in design limitation as far as handling/performance is concerned. This is why enthusiast drivers tend to shun FWD-equipped cars. It is fundamentally an economy-oriented drivetrain layout designed to cut manufacturing/assembly costs.

The lowdown: FWD is a good choice for the average driver who uses his vehicle to get from "a" to "b" and would like to have decent traction on those few days each winter when there's some snow on the roads.

All-wheel-drive (AWD)
This is a system in which engine power can be sent to all four wheels (or to individual wheels/pairs of wheels) as necessary to maintain traction. As recently as five or six years ago, only a few makes/models offered AWD systems; today, AWD is either standard or available optionally on many types of passenger cars, wagons, minivans and light-duty, car-based "crossovers."

The upside: AWD provides excellent all-year/all-weather grip -- on snow-covered roads in winter and on dry (or wet) paved roads in summer. And unlike a truck-style 4x4 system, AWD is optimized as much for use on smooth, paved surfaces as it is for use in snow (or unpaved gravel and dirt). High-performance AWD-equipped sports cars and sedans offer incredible dry-weather, on-road handling with superior wintry weather capability. Also, AWD systems do not require any driver involvement; power is automatically routed to the wheels with the most traction -- typically via a device known as a viscous coupling. Modern systems are highly efficient and there is usually very little fuel economy penalty vs. a FWD (or rear-wheel-drive) vehicle.

The downside: Like FWD, AWD is not designed for severe off-road use; there is no two-speed transfer case or 4x4 Low-range gearing. AWD can also add substantially to the purchase price of the vehicle -- sometimes by as much as several thousand dollars.

The lowdown: AWD is an excellent choice for the enthusiast-oriented driver who values dry-weather handling and lateral grip in a high-speed corner as much as being able to get out of his driveway when it snows.

Rear-wheel drive (RWD)
This was once the standard drivetrain layout of most passenger cars, especially domestic-brand models. The engine is up front -- but power is sent to the rear wheels exclusively.

The upside: Rear-drive cars spread the weight of the engine, transmission and axle assemblies front to rear more evenly than nose-heavy FWD cars -- and tend to be lighter (and cheaper to buy/maintain) than AWD-equipped cars. Rear-drive cars are also rugged and durable -- which is why they are favored for police/taxi duty. And finally, rear-drive allows for smoky burnouts and tire-skittering hooliganism -- important to many performance car enthusiasts.

The downside: A RWD vehicle is not the hot ticket for snow driving -- unless you enjoy fishtailing like a just-landed sea bass. Rear-drive (2WD) pick-ups are especially atrocious; their light rear ends tend to break loose alarmingly even on wet roads. Snow driving is a complete white-knuckler.

The lowdown: If you live in Arizona, New Mexico or Florida -- or enjoy a good burnout every now and then -- rear-drive will probably suit you fine. But don't expect to get anywhere (except perhaps the body shop) if you have to deal with the white stuff!
 




smilefrog

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Hello!! I just purchased a '96 Explorer XLT V8 with AWD. I got a great deal because the transefer case is apparently not quite right. Upon acceleration from a standstill, it jumps, like it's going over a bump. I'm wondering if anyone else has experienced this and if it could potentially be something other than the transfer case, like an axle or something else?? I hope it won't be too difficult or expensive to fix. Also, if you know of someone who rebuilds transfer cases or axles that would work in this Explorer, please let me know in case either or both need to be exchanged.
Thank You!!
:)Heather
 




nothin special

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is there a loud bang when it jumps from a stand still, my '93 used to do the same thing, it was my tranny going bad. of course that was my '93 which has a different tranny, but it's an idea.
 




dixon95

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I have 02 thats has that auto 4-wheel drive. I can hear it grinding or engaging when i am on payment or even at a stop getting ready to turn. No warning lights have gone off. The diff. was replace by ford with 29000 miles on it. I love the vehicle but this does not sound good. Seems like it getting louder. I friend said a sensor might be going bad. Or is there a way to disconnect the auto 4 wheel drive.

David
 




AMMO_HOOAH

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smilefrog said:
Hello!! I just purchased a '96 Explorer XLT V8 with AWD. I got a great deal because the transefer case is apparently not quite right. Upon acceleration from a standstill, it jumps, like it's going over a bump. I'm wondering if anyone else has experienced this and if it could potentially be something other than the transfer case, like an axle or something else?? I hope it won't be too difficult or expensive to fix. Also, if you know of someone who rebuilds transfer cases or axles that would work in this Explorer, please let me know in case either or both need to be exchanged.
Thank You!!
:)Heather

My '96 did the same thing it was the t/c. The PTU was completly destroyed, and the chain had like a full inch in slack. I'd say your best bet would be to find a used one for cheap, because rebuilt ones/new ones are pretty spendy $1,000^^^ You could try and have someone rebuild it, but I have no idea on the cost. I picked my used one up for $200. Good luck!
 




Rayulty

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have a 96 explorer limited

everytime I accelerate
the whole vehicle jerks when I reach the spead of 50-60 km
and makes a loud clicking noise
it does the same at 70 km
the same problem is also experienced while slowing down

could it be the transfer case

please help
 


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bigbandit said:
I've tried lifting all 4 wheels clear of the ground and spinning them. Then trying to shift back into 2wd, but it is still in 4wd and in low range. Any other suggestions.
-Kev. :(
Have you tried making sure the transmission is in neutral before attempting a range shift? The electronic systems will not allow a range shift in Park and usually not in any gear. (Range being from lo to hi or hi to lo) I have seen this concern come up at our shop more then once, frequently because the operator does not understand how the system is designed to work.
 




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