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Check shift fork operation....
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Section 07-07: Transfer Case, 4x4 System, Service
1996 F-150, 250, 350 (4x4), and Bronco Vehicles with Manual Shift Transfer Case; All Bronco and F-150 4x4 Vehicles with Electronic Shift Transfer Case Only Workshop Manual
DESCRIPTION AND OPERATION
Mechanical Operation
In the 4x2 mode, torque from the transmission (7003) is transferred to the front input shaft, which in turn drives the output and fifth gear drive shaft (7061) that drives the rear axle.
The 2W-4W shift is accomplished when the 2W-4W shift fork moves the lockup collar to engage the drive sprocket on the rear output shaft splines. The drive sprocket turns the chain which turns the front output shaft driven sprocket on the front output and fifth gear drive shaft and the front driveshaft.
The high-low shift is accomplished when the high-low shift fork moves the shift collar hub to engage the front planet (7A398) to the output and fifth gear drive shaft. Torque for the input shaft (7017) is then transmitted through the sun gear, which then turns the front planet. The front planet, which is now engaged to the output and fifth gear drive shaft, provides a reduction.
Neutral
With the shift selector in neutral, no power is transmitted to either front or rear. All the planetary gears turn freely with the input shaft, and the chain sprocket floats freely on the output and fifth gear drive shaft.
Power Flow in Neutral
The following illustration shows a cross-section of the front planet. At the center, attached to the input shaft, is the sun gear. This gear meshes with four gears that surround it like planets (which is why this component is called a planetary gear). In turn, the four gears mesh with an outer gear called the ring gear (7A153).
The sun gear rotates at the speed of the transmission output. The ring gear is stationary. The front planet assembly rotates with the planetary gears as they "walk" around the inside of the ring gear to provide the gear reduction. If the output shaft is locked to the sun gear, as in high range, the output rotates at transmission output speed. If the output is locked to the front planet assembly, as in low range, the output rotates at the reduction rate.
2-Wheel Drive — High Range
When the driver selects 2H, the shift collar hub at the center of the front planet slides forward, putting the transfer case (7A195) into the high speed range (direct drive). The input shaft and the rear output shaft are locked together. This results in direct drive, straight through to the rear driveshaft. In addition, the 4-wheel drive lockup collar is disengaged so none of the 4WD components turn.
Power Flow in 2H
See diagrams
http://www.diesel-dave.com/vehic/manual/stj/stj77003.htm
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Section 07-07: Transfer Case, 4x4 System, Service
1996 F-150, 250, 350 (4x4), and Bronco Vehicles with Manual Shift Transfer Case; All Bronco and F-150 4x4 Vehicles with Electronic Shift Transfer Case Only Workshop Manual
DESCRIPTION AND OPERATION
4x4 Vehicle — Driveline Windup
Driveline windup does more than just produce hop, skip and bounce. It can also cause delays in shifting out of 4WD. Vehicles with electronic shift transfer case (7A195) permit shifting from 2WD to 4WD and back on the fly. The vehicle must be stopped and the automatic transmission (7003) put in neutral (not park) or the manual transmission clutch depressed in order to shift from 4H to 4L or back.
http://www.diesel-dave.com/vehic/manual/stj/stj77006.htm
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System, Service
1996 F-150, 250, 350 (4x4), and Bronco Vehicles with Manual Shift Transfer Case; All Bronco and F-150 4x4 Vehicles with Electronic Shift Transfer Case Only Workshop Manual
DESCRIPTION AND OPERATION
Windup and Delay — Shifting Out of 4-Wheel Drive
NOTE: To determine if driveline windup is causing delayed shifts to 2WD, jack the vehicle or lift it on a hoist with the wheels free to rotate. This should release the driveline windup, if it is present, and the transfer case (7A195) will complete its shift, if windup is the concern.
NOTE: Vehicles vary in terms of how "tight" they are. Some vehicles have a lot of "give" in the system. Softness in suspension and mounts will allow the driveline to absorb more windup before it affects performance. If driveline windup occurs, the system will tighten like a giant rubber band until the tires start slipping. A "tight" vehicle will signal the windup sooner, usually by a lot of chattering noises.
A delay or a failure to shift out of 4WD may be the result of driveline windup or extremely cold temperatures. In 4WD, windup can develop, especially if the vehicle is operated on hard, dry surfaces or in tight turns. The driver may select 2WD, but the shift doesn't take place even though the 4WD light goes out. Also, as long as the transfer case doesn't shift, the hubs remain locked and the vehicle remains in 4WD. If windup in the transfer case is severe, even backing up may not release it.
In order to return to 2WD under these conditions, two things must happen. First, if the transfer case doesn't shift right away, the vehicle will have to be driven in 4WD until the windup is relieved or until the axle warms up. Second, when it does make the shift, the driver will have to stop the vehicle and go straight in the reverse direction for at least ten feet to unlock the hubs.
http://www.diesel-dave.com/vehic/manual/stj/stj77007.htm
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4-Wheel Drive — High Range
In 4-wheel drive — high range (4H), the front planet stays where it was in the 2H shift. The action of the shift lever causes the 4-wheel drive lockup hub to move rearward, locking the chain sprocket to the rear output shaft. Now, both the rear and the front wheels are being driven in the high range.
Power Flow in 4H
http://www.diesel-dave.com/vehic/manual/stj/stj77003.htm#extract_1194
