4X4 Transmission Question
Question:
>I’m curious about the electronic clutch activation in the transfer case. >These descriptions say that the front driveshaft is automatically engaged at >a minimal level. In previous posts, people have asked about replacing their >front hubs. The stock hubs are automatic locking (which I assume means that >they automatically lock themselves to the axle for 4WD mode). A cheap >replacement for the auto hubs is a manual hub which must be manually locked >in. So does this mean that if the front manual hubs aren’t locked in, that >the transfer case will still periodically engage the clutch causing the >front drive shaft to spin with nothing connected to it?
I dunno the answer to that one. >In addition to that, the 4WD system doesn’t seem to be operating correctly >on my 97 Limited 4.0 SOHC. I can only choose from 4WD auto, 4WD high, and >4WD low. When in auto, if I encounter a slippery slope the truck just sits >there and the back tires spin, fronts don’t move. If I put it into 4WD >high, the truck will start to move, but I have gotten stuck before and then >I hear a wheel spinning, 2 of the 4 tires have been spinning and the other 2 >just sat there, no movement. I’m sure this is due to the differentials, but >it sucks that 2 slipping tires leaves me stuck.
When in 4Auto (I think it’s called A4WD) the clutch is modulated to provide controled HP to the front axle. If you have NO front wheels turning in this situation, the system’s broke. Yes, it sucks that, when in 4WD, 2 slipping wheels (one on each axle) can leave you stuck. That’s why most 4WD vehicles have limited slip rear diffs. That’s why extreme 4wheelers use locker diffs; with a locker both front and rear, all 4 wheels get power, all the time. And turning is a bitch. Limit3ed slip front diffs are not a good idea on street-driven vehicles, that’s why they aren’t seen but very seldomly. They make steering very interesting on less than perfect pavement. If you are running into situations where you get stuck from spinning wheels, you may be a candidate for a locker rear differential. >Can anyone give me more info? >Dave Earle >97 Explorer Limited >87 GT Convertible
– Bill Replace "g" with "a" Experience is what you get when you expected something else.
Response:
On the ‘97, there are no "locking hubs", neither automatic or otherwise. 4WDs will have an "axle lock" on the right hand axle tube – IIRC it is vacuum operated. Not enough familiarity with the AWD to comment further. — Jim Warman
– Hide quoted text — Show quoted text -> I’m curious about the electronic clutch activation in the transfer case. > These descriptions say that the front driveshaft is automatically engaged at > a minimal level. In previous posts, people have asked about replacing their > front hubs.
Response:
>What happens in 4×4 Auto when going downhill and the rear tires slip?
You skid? Why would the rear tires slip going downhill? If they slip under braking, you’re already in trouble; slow down. If they slip because you’ve got it in 1st gear, go to 4×4 HI; this will provide equal retardation for the front & rear wheels. Does this make sense? — Bill Replace "g" with "a" Experience is what you get when you expected something else.
Response:
What happens in 4×4 Auto when going downhill and the rear tires slip? – Hide quoted text — Show quoted text -> Here is an explanation for you: > The 4WD system you have is what Ford calls Control Trac. The Control Trac > system uses an electrically controlled clutch in the transfer case to engage > the front wheels. Normally in a typical part time 4 wheel drive system in > 2-High mode, only the rears would be mechanically connected to the > engine/transmission, with the front drive train freewheeling. > Now, keep in mind that when you turn, the front wheels must travel farther > than the rear ones, since the actual turning circle for the outside front > wheel is larger than for the inside rear (actually, each wheel travels at a > different speed through a turn, and the difference depends on the tightness > of the turn). This is important on 4WD vehicles. Keep it in mind throughout > the rest of this description. > In 4-High, the clutch in the transfer case is fully engaged, and the front > drive train is locked "in step" with the rear, that is, the front axle turns > at the same speed as the rear. If you try to turn on solid ground such as > wet or dry road surfaces, there is binding as the front wheels try to turn > faster than the rear but cannot. Something has to give, and it could be the > tires sliding and jumping across the pavement or it could be a broken axle > shaft, drive shaft, or other part. This is why you shouldn’t use 4-High on > the road unless it is quite slippery. > The same holds true for 4-Low. A different gear is used in 4-Low to allow > for steep hill climbing and descending in low range, but like 4-High, the > front and rear drive trains are locked together through the electric clutch > in the transfer case. > Now, in the Auto mode, things get more complicated. While the rear axle is > the primary drive axle, the fronts do have some power applied as well. This > is controlled electronically. The GEM module (I think that stands for > generic electronic module) actually continually pulses the electric clutch > such that it is engaged for short bursts, long enough to allow some drive > forces to go through the front axle, but short enough to relieve the binding > that can occur when turning. These pulses can occur several times a second. > Now, when traction is good, these short periods of engagement occur such > that the front axle is engaged approximately 5% of the time. That is where > Ford gets the 95% rear/ 5% front power transfer levels. > When things get a little more slippery, the system reacts. The wheel speed > sensors that are part of the ABS system (anti-lock brakes) are used to > detect rear wheel spin. If the computer senses that the rear wheels are > turning faster than the front wheels, the computer automatically tells the > clutch to be engaged for a longer portion of the time. This is done in 10% > increments, up to a duty cycle of 100%. (It will go to 15% front/ 85% rear > and so on until traction is regained.) The change begins to occur within > about 1/5 of a turn of the loose or spinning rear wheel. By increasing > engaged time in small increments, the system can apply just enough torque to > the front axle to give you added traction, while allowing periods of relief > for the drive train to prevent binding. These engage/disengage pulses occur > several times per second. > Once traction is regained and the wheels are turning at the same speed (the > rears are no longer turning faster than the front wheels), the procedure > reverses itself, once again in 10% increments. This continues over a period > of a couple of minutes until the power distribution is back to the 5% front/ > 95% rear ratio. > PS AWD gives a permanent 50/50 power split from front to rear. > Hope this helps > I have a 2002 Explorer XLT. It has 3 transmission modes: 4X4 AUTO, 4X4 > question is: Is 4X4 AUTO the same as the AWD I had with my 1997 XLT? If > not, what are the differences? > Thanks much, > Al/Poughkeepsie
Response:
I’m curious about the electronic clutch activation in the transfer case. These descriptions say that the front driveshaft is automatically engaged at a minimal level. In previous posts, people have asked about replacing their front hubs. The stock hubs are automatic locking (which I assume means that they automatically lock themselves to the axle for 4WD mode). A cheap replacement for the auto hubs is a manual hub which must be manually locked in. So does this mean that if the front manual hubs aren’t locked in, that the transfer case will still periodically engage the clutch causing the front drive shaft to spin with nothing connected to it? In addition to that, the 4WD system doesn’t seem to be operating correctly on my 97 Limited 4.0 SOHC. I can only choose from 4WD auto, 4WD high, and 4WD low. When in auto, if I encounter a slippery slope the truck just sits there and the back tires spin, fronts don’t move. If I put it into 4WD high, the truck will start to move, but I have gotten stuck before and then I hear a wheel spinning, 2 of the 4 tires have been spinning and the other 2 just sat there, no movement. I’m sure this is due to the differentials, but it sucks that 2 slipping tires leaves me stuck. Can anyone give me more info? Dave Earle 97 Explorer Limited 87 GT Convertible – Hide quoted text — Show quoted text -> In the Auto mode, torque from the transmission is transferred to the input > shaft which, in turn, drives the rear output shaft that drives the rear > axle assembly. The electromechanical ball ramp clutch assembly drives the > drive sprocket after the 4×4 electronic module activates the clutch coil. The > drive sprocket turns the drive chain that rotates the front output shaft and > the front driveshaft. In the 4×4 High mode, the operation is the same as in > the Auto mode, except that the 4×4 electronic module consistently activates > the electromechanical ball ramp clutch assembly. > Control-Trac Function > The Control-Trac transfer case uses an electromechanical clutch assembly to > control torque to the front wheels. In the Auto mode, while at rest > and under cruising conditions, the 4×4 electronic module activates the > transfer case clutch at a minimum level. This allows for the slight > difference between the front and rear driveshafts which occurs normally when > negotiating a corner on dry pavement. Under any of the following conditions, > the 4×4 electronic module will increase the torque sent through the clutch to > the front wheels in order to prevent or control slip.
Response:
> I have a 2002 Explorer XLT. It has 3 transmission modes: 4X4 AUTO, 4X4 > question is: Is 4X4 AUTO the same as the AWD I had with my 1997 XLT? If > not, what are the differences?
If you had a 1997 with a V-8 you had AWD. The 1997 six cylinders got Command-Trac (if they were 4WD). The AWD system doesn’t split the torque 50-50. It splits it 35 front, 65 rear. Previously I posted the explanation from the Ford Service CD. Here it is again. The 2002 is similar, although some of the exact details may vary slightly. 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 constantly activated, automatic, all-wheel drive transfer case has no external controls. A two-piece aluminum case houses the assembly. The unit is chain driven. A non-repairable viscous coupling provides torque distribution to the front and rear transfer case outputs. The viscous coupling contains slotted alternating plates through which a high viscosity fluid flows. The resistance of the fluid shear causes the plates to transmit torque at the approximate ratio of 35 percent to the front output and 65 percent to the rear output. Operation Torque flows through the input shaft to the front planetary gear assembly outward to the ring gear to the upper output shaft. Torque also flows through the front planetary gear assembly to the overdrive sun gear outward to the upper drive sprocket. The torque flow continues from the upper drive sprocket through the drive chain to the lower drive sprocket to the front output shaft. The viscous coupling provides the connection between the ring gear and the overdrive sun gear. Four-Wheel Drive Systems Automatic Four Wheel Drive (A4WD) The automatic four-wheel drive (A4WD) system is an electronic shift 4X4 system that utilizes the following components: -transfer case -four-wheel drive (4WD) control module -mode select switch (MSS) -gearmotor encoder assembly -electric shift motor (part of gearmotor encoder assembly) -shift motor sense plate (part of gearmotor encoder assembly) Transfer Case Motor, Electric Shift The externally mounted transfer case shift motor, located at the rear of the transfer case, turns the shift cam assembly. As the shift cam assembly turns, it positions the reduction shift fork for desired transfer case operation. An integral position sensor in the shift motor provides motor position information to the 4×4 electronic module. Switch, Push Button 4×4 Mode The push button 4×4 mode switch, mounted on the instrument panel, allows the operator to select the 4×4 Auto, 4×4 High, and 4×4 Low transfer case operating modes. The indicator light, on the instrument cluster push button, will illuminate only when the 4×4 Low position is engaged. Switch, Brake Pedal Position (BPP) The brake pedal position (BPP) switch is located on the brake pedal. The switch signals the 4×4 electronic module when the operator activates the brake pedal. Switch, Clutch Pedal Position (CPP) The clutch pedal position (CPP) switch is located on the clutch pedal bracket. On vehicles equipped with a manual transmission and an electronic shift transfer case, the clutch pedal must be fully depressed and vehicle stopped in order to make a range shift from HIGH to LOW, or from LOW to HIGH. Sensor, Digital Transmission Range (DTR) The DTR sensor is located on the outside of the transmission near the transmission shift cable attachment. The DTR sensor completes the start circuit in PARK and NEUTRAL, the back-up lamp circuit in REVERSE and the neutral sense circuit (4WD) in NEUTRAL. The DTR sensor also sends a digital output signal to the powertrain control module (PCM) indicating the manual lever position (P, R, N, D, 2, 1). Sensor, Throttle Position (TP) The TP sensor is located on the throttle body. The sensor provides throttle position information to the PCM. The PCM converts the throttle position signal to a pulse width modulated (PWM) signal, and sends it to the 4×4 electronic module to control and adjust the transfer case clutch duty cycle. Sensor, Front and Rear Output Shaft Speed (OSS) The externally mounted OSS sensors are located at the rear of the transfer case. The sensors provide the 4×4 electronic module with front and rear driveshaft speeds to control and adjust the transfer case clutch duty cycle. Sensor, Vehicle Speed Sensor (VSS) The Anti-Lock Brake System (ABS) provides the 4×4 electronic module with vehicle speed information to control and adjust the transfer case clutch duty cycle. 4×4 Electronic Module The electronic module (located behind the glove compartment) controls the operation of the transfer case in response to inputs from the electric shift motor, 4×4 mode switch, CPP switch, BPP switch, DTR sensor, throttle position output from the PCM, front and rear OSS sensors, and the VSS. Mechanical Operation The Borg-Warner 44-11 transfer case is available in the Explorer (A4WD) vehicle. The transfer case transfers power from the transmission to the rear axle, and also to the front axle when electronically activated. In the Auto mode, torque from the transmission is transferred to the input shaft which, in turn, drives the rear output shaft that drives the rear axle assembly. The electromechanical ball ramp clutch assembly drives the drive sprocket after the 4×4 electronic module activates the clutch coil. The drive sprocket turns the drive chain that rotates the front output shaft and the front driveshaft. In the 4×4 High mode, the operation is the same as in the Auto mode, except that the 4×4 electronic module consistently activates the electromechanical ball ramp clutch assembly. The high-low shift occurs when the reduction shift fork moves the high-low collar to lock the planetary gear set to the output shaft. Then, torque, transmitted through the sun gear, from the input shaft, turns the front planetary gear set assembly. The front planetary gear set assembly, which is now engaged, provides transfer case speed reduction. Transfer Case Functions There are three transfer case modes, Auto, 4×4 Low, and 4×4 High. Neutral is only available as a dealer installed option. Control-Trac Function The Control-Trac transfer case uses an electromechanical clutch assembly to control torque to the front wheels. In the Auto mode, while at rest and under cruising conditions, the 4×4 electronic module activates the transfer case clutch at a minimum level. This allows for the slight difference between the front and rear driveshafts which occurs normally when negotiating a corner on dry pavement. Under any of the following conditions, the 4×4 electronic module will increase the torque sent through the clutch to the front wheels in order to prevent or control slip. – Slip is detected (by monitoring the front and rear OSS sensors in the transfer case) – Throttle position (by using the throttle position signal from the PCM) Range Function NOTE: At zero throttle, the duty cycle remains low. In the 4×4 Low Range, with throttle input, the transfer case electromechanical clutch locks the front and rear driveshafts for maximum 4×4 traction. The transfer case shift motor rotates the shift cam to move the reduction shift fork to the 4×4 Low range position. This low range shift, accomplished through a planetary gear set, changes the torque to the driveshaft from 1:1 to 2.48:1 ratio. In the 4×4 High Range, with throttle input, the 4×4 electronic module signals the transfer case electromechanical clutch to lock the front and the rear driveshafts for maximum 4×4 traction. Never use the 4×4 High range or the 4×4 Low range when driving on dry or merely wet pavement. Use the 4×4 High range or the 4×4 Low range only for driving off-road or in severe winter weather. Regards, Ed White
Response:
Here is an explanation for you: The 4WD system you have is what Ford calls Control Trac. The Control Trac system uses an electrically controlled clutch in the transfer case to engage the front wheels. Normally in a typical part time 4 wheel drive system in 2-High mode, only the rears would be mechanically connected to the engine/transmission, with the front drive train freewheeling. Now, keep in mind that when you turn, the front wheels must travel farther than the rear ones, since the actual turning circle for the outside front wheel is larger than for the inside rear (actually, each wheel travels at a different speed through a turn, and the difference depends on the tightness of the turn). This is important on 4WD vehicles. Keep it in mind throughout the rest of this description. In 4-High, the clutch in the transfer case is fully engaged, and the front drive train is locked "in step" with the rear, that is, the front axle turns at the same speed as the rear. If you try to turn on solid ground such as wet or dry road surfaces, there is binding as the front wheels try to turn faster than the rear but cannot. Something has to give, and it could be the tires sliding and jumping across the pavement or it could be a broken axle shaft, drive shaft, or other part. This is why you shouldn’t use 4-High on the road unless it is quite slippery. The same holds true for 4-Low. A different gear is used in 4-Low to allow for steep hill climbing and descending in low range, but like 4-High, the front and rear drive trains are locked together through the electric clutch in the transfer case. Now, in the Auto mode, things get more complicated. While the rear axle is the primary drive axle, the fronts do have some power applied as well. This is controlled electronically. The GEM module (I think that stands for generic electronic module) actually continually pulses the electric clutch such that it is engaged for short bursts, long enough to allow some drive forces to go through the front axle, but short enough to relieve the binding that can occur when turning. These pulses can occur several times a second. Now, when traction is good, these short periods of engagement occur such that the front axle is engaged approximately 5% of the time. That is where Ford gets the 95% rear/ 5% front power transfer levels. When things get a little more slippery, the system reacts. The wheel speed sensors that are part of the ABS system (anti-lock brakes) are used to detect rear wheel spin. If the computer senses that the rear wheels are turning faster than the front wheels, the computer automatically tells the clutch to be engaged for a longer portion of the time. This is done in 10% increments, up to a duty cycle of 100%. (It will go to 15% front/ 85% rear and so on until traction is regained.) The change begins to occur within about 1/5 of a turn of the loose or spinning rear wheel. By increasing engaged time in small increments, the system can apply just enough torque to the front axle to give you added traction, while allowing periods of relief for the drive train to prevent binding. These engage/disengage pulses occur several times per second. Once traction is regained and the wheels are turning at the same speed (the rears are no longer turning faster than the front wheels), the procedure reverses itself, once again in 10% increments. This continues over a period of a couple of minutes until the power distribution is back to the 5% front/ 95% rear ratio. PS AWD gives a permanent 50/50 power split from front to rear. Hope this helps – Hide quoted text — Show quoted text -> I have a 2002 Explorer XLT. It has 3 transmission modes: 4X4 AUTO, 4X4 > question is: Is 4X4 AUTO the same as the AWD I had with my 1997 XLT? If > not, what are the differences? > Thanks much, > Al/Poughkeepsie
Response:
I have a 2002 Explorer XLT. It has 3 transmission modes: 4X4 AUTO, 4X4 question is: Is 4X4 AUTO the same as the AWD I had with my 1997 XLT? If not, what are the differences? Thanks much, Al/Poughkeepsie
Response:
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