It's wierd, I've looked all over the web, I've looked on the ford website, Ive emailed a ford dealer ship, I bought car and driver's guide to suv's, no matter what the source i can't find information on the Explorer's all wheel drive system. There's just no info. Even the C&D guide which gives a good description of every SUV's system, only mentions the 4 wheel drive explorer. Do any of you know how the system works. Center differential, viscous coupling, geroter pump? This is a real challenge for you real explorer enthusiasts. Thanks

 

I've always assumed that the AWD in the 2002/ 2003 Explorers is the same unit that went into the earlier ('96-'01) models. Here's some info I received in January of 1996 when the AWD model was first introduced:

" the transfer case is a Borg-Warner make. It is the same case GMC used in the S15 Typhoon hot-rod. Usage indicates exceptional reliability. The AWD does not have a center disconnect as does a 4WD. The AWD is a single-speed transfer case. Therefore, the AWD does not have a low range like 4WD. Under severe off-road conditions, the AWD would not perform like the 4WD low range.

....the AWD functions like this: the transfer case has no driver input; i.e., no switch. Thirty-five percent of the torque is distributed to the front axle; sixty-five percent to the rear axle at all times. When wheel slippage occurs, the viscous clutch in the transfer case transfers more torque to the axle that has the most traction.....35% torque to the front/ 65% to the rear is a measurement under normal conditions. If the front end was affected by icy road conditions, where the transfer case clutch transferred the maximum torque to the front axle, the ratio could be 50/50 or even 65% (front) and 35% (rear). According to Ford Engineering personnel, AWD testing in off-road dirt/ sand conditions, the AWD performed superbly."

Again, I'm assuming that this is the same system currently in use, but I could be mistaken. If anyone has any further info, by all means share it with us.

 

This is from the 2002 ford service Manual

Four-Wheel Drive Systems — All-Wheel Drive (AWD)

The all-wheel drive (AWD) system utilizes a transfer case that is a two-piece aluminum, chain-driven, viscous clutch-type unit. This results in a system in which AWD is always activated. The AWD transfer case is automatic and has no external controls.

The all-wheel drive system utilizes a transfer case that is a two-piece aluminum, chain-driven, viscous-clutch type unit. This results in a system in which all-wheel drive is always activated. The all-wheel drive transfer case is automatic and has no external controls.

The viscous clutch is a torque distribution device. It is non-repairable. The internal construction of the viscous clutch consists of alternating plates that are connected to the front and rear outputs of the transfer case. The viscous clutch is filled with a high viscosity fluid which flows through slots in the plates. The resistance to shear causes the plates to transmit torque at the needed ratio. The ratio that torque is transmitted at is approximately 35% front and 65% rear.

Torque is transmitted through the input shaft to the planet carrier assembly. Torque flow continues through the gear ring to the rear output shaft. Torque also flows from the planet carrier assembly to the sun gear shaft, which is splined to the drive sprocket. The drive gear is connected to the driven sprocket by the drive chain. Torque continues through the driven sprocket to the front output shaft flange. The viscous clutch provides the connection between the gear ring and the sun gear shaft.

 

You didn't ask But is the a4wd skinny

he automatic four-wheel drive (A4WD) system is an electronic-shift 4X4 system that allows the operator to choose between three different 4X4 modes. The operator can switch between 4X4 AUTO and 4X4 HIGH modes at any speed. To engage or disengage 4X4 LOW range, the vehicle speed must be less than 5 km/h, the brake pedal must be depressed, and the transmission must be in NEUTRAL.

The front and rear shaft speed sensors (Hall-effect) are mounted to the transfer case and detect the speed of the front and rear transfer case driveshafts. This input is used by the four-wheel drive (4WD) control module to control 4WD operation.

The throttle position output signal is provided to the 4WD control module from the powertrain control module (PCM). This signal is used by the 4WD control module in controlling the 4WD clutch.

The shift motor sense plate, an integral part of the gearmotor encoder assembly, informs the 4WD control module of the transfer case position.

The digital transmission range (TR) sensor is located on the LH side of the transmission; this sensor informs the 4WD control module when the transmission is in NEUTRAL.

The electric shift motor is mounted externally to the gearmotor encoder assembly at the rear of the transfer case. It drives a rotary cam which moves the mode fork and range fork within the transfer case between the HIGH range (4X4 AUTO, 4X4 HIGH) and 4X4 LOW range positions.

The 4X4 shift motor is controlled by the 4WD control module which shifts the transfer case shift motor between HIGH range (4X4 AUTO, 4X4 HIGH), and 4X4 LOW modes.

 

Thank both of you. Knowing how these systems work will definitely help me in the future. I was never quite sure of any lage that might have been experienced with an AWD system. I've heard viscous coupling was a reactive system and therefore not very good for four wheel drive. But knowing that there is always the 35 % of the torque being applied to the front wheels is much more confidence inspiring. Thanks again.

 

Out of curiousity...

I haven't needed 4low in my 98 5.0 AWD, but I haven't put it to the supreme test.

Has anyone looked into swapping the Expedition's A4WD into a 5.0 AWD Explorer?