Will not shift into 4-wheel drive

Which 4X4 system does yours have ?
Four-Wheel Drive Systems The mechanical-shift 4-wheel drive system consists of the following components:

• Transfer case (For transfer case repair procedures, refer to Section 308-07B ).
• Transfer case shift lever
• Manual locking hubs
• 4x4 indicators
• Shift linkage (hub locks)

The electronic-shift, 4-wheel drive system consists of the following components:

• Transfer case (For transfer case repair procedures, refer to Section 308-07B ).
• Four-wheel drive (4WD) control module (For 4WD control module installation, refer to 4WD control module in this section.)
• Mode select switch (MSS)
• Gearmotor encoder assembly
• Automatic locking hubs (hub locks)
• Pulse vacuum hub lock (PVH) solenoid and vacuum lines

Have it check for DTC'S - diagnostic trouble codes ?
GEM Diagnostic Trouble Code (DTC) Index
GEM Diagnostic Trouble Code (DTC) Index DTC Description Source Action C1728 Transfer Case Unable to Transition Between 2H and 4H GEM CARRY OUT the electronic shift function test. REFER to Function Test - Electronic Shift in this section. C1729 Transfer Case Unable to Transition Between 4H and 4L GEM CARRY OUT the electronic shift function test. REFER to Function Test - Electronic Shift in this section. P0500 Vehicle Speed Sensor (VSS) Malfunction GEM GO to Pinpoint Test F . P1804 Transmission 4-Wheel Drive High Indicator Circuit Failure GEM GO to Pinpoint Test H . P1808 Transmission 4-Wheel Drive Low Indicator Circuit Failure GEM GO to Pinpoint Test I . P1812 Transmission 4-Wheel Drive Mode Select Circuit Failure GEM GO to Pinpoint Test E . P1815 Transmission 4-Wheel Drive Mode Select Short Circuit to Ground GEM GO to Pinpoint Test E . P1819 Transmission Park/Neutral Position Switch Short Circuit to Ground GEM GO to Pinpoint Test F . P1820 Transmission Transfer Case Clockwise Shift Relay Coil Circuit Failure GEM GO to Pinpoint Test E . P1822 Transmission Transfer Case Clockwise Shift Relay Coil Short to Battery GEM GO to Pinpoint Test E . P1828 Transfer Case Counterclockwise Shift Relay Coil Circuit Failure GEM GO to Pinpoint Test E . P1830 Transmission Transfer Case Counterclockwise Shift Relay Coil Short Circuit to Battery GEM GO to Pinpoint Test E . P1832 Transmission Transfer Case Differential Lockup Solenoid Circuit Failure GEM GO to Pinpoint Test G . P1834 Transmission Transfer Case Differential Lockup Solenoid Short Circuit to Battery GEM GO to Pinpoint Test G . P1865 Transmission Transfer Case Contact Plate Power Short to Ground GEM GO to Pinpoint Test E . P1866 Transmission Transfer Case System Concern - Servicing Required GEM CARRY OUT the electronic shift function test. REFER to Function Test - Electronic Shift in this section. P1867 Transmission Transfer Case Contact Plate General Circuit Failure GEM GO to Pinpoint Test E . P1876 Transmission Transfer Case 2-Wheel Drive Solenoid Circuit Failure GEM GO to Pinpoint Test G . P1877 Transmission Transfer Case 2-Wheel Drive Solenoid Circuit Short to Battery GEM GO to Pinpoint Test G . - For All Other DTCs GEM GO to Section 419-10 .
Your best bet , take it to a qualified repair shop that has the diagnostic tool to trouble shoot .
Principles of Operation
Transfer Case - Electronic Shift
The four-wheel drive, electronic shift-on-the-fly feature electrically shifts the vehicle transfer case between 2WD, 4X4 HIGH, and 4X4 LOW. The system mode is selected by the operator through the mode select switch (MSS) on the instrument panel. The operator is informed which mode the system is in by two instrument cluster indicators, one for 4X4 HIGH which is 4X4, and one for 4X4 LOW which is LOW RANGE (in 4X4 LOW both the lamps are on). Shifts into 4X4 HIGH can be made at any speed. When shifting into 4X4 HIGH with the vehicle stationary, tooth blockage may occur, preventing shift completion. When the vehicle is driven above 8 km/h (5mph) the shift will complete. When shifting in or out of 4X4 LOW, the generic electronic module (GEM) requires that the vehicle speed be less than 5 km/h (3 mph), the brake pedal be applied, and the transmission in NEUTRAL (automatic transmission) or the clutch pedal be depressed (manual transmission). (The digital transmission range [TR] sensor informs the GEM when the automatic transmission is in the NEUTRAL range position.)
The gearmotor encoder assembly is mounted externally on the transfer case. It drives a rotary cam which moves the mode fork and the range fork within the transfer case between the 4X4 HIGH, 4X4 LOW, and 2WD range positions.
The GEM uses two relays to control the gearmotor encoder assembly shift between 4X4 HIGH, 4X4 LOW, and 2WD modes. The GEM controls the pulse vacuum hublock (PVH) solenoid which supplies engagement and disengagement vacuum to control the hublocks.
The GEM accomplishes shifts by interpreting inputs from:

• mode select switch (MSS)
• vehicle speed signal (transmitted from the ABS system)
• gearmotor encoder plate position
• brake pedal switch
• digital transmission range (TR) sensor (automatic transmission)
• clutch pedal position (CPP) switch (manual transmission)
• ignition switch

Based on these inputs, the GEM controls the shifts into 2WD, 4X4 HIGH, or 4X4 LOW with the following outputs:

• low to high relay (clockwise)
• high to low relay (counterclockwise)
• pulse vacuum hublock (PVH) solenoid
• gearmotor encoder assembly

The electronic shift-on-the-fly (ESOF) system has a feature which allows the driver to override the vacuum operated hublocks. When the front hublocks are manually turned to the LOCK position, the hublocks are locked at all times, overriding the vacuum operated system. If the front hublocks are manually turned to the AUTO position, the hublocks can only be locked by turning the MSS to 4X4 HIGH or 4X4 LOW position.

Automatic, or Standard? Last time transmission serviced? If auto, check fluid, if smells burnt, get serviced. However,it sounds like a problem in the linkage/s from the shift lever to the transmission and 4wheel controls.

The 4X4 system on your vehicle is computer controlled , GEM module . generic electronic module . The four wheel drive mode switch is a low voltage input to the GEM module . The GEM energizes relay's to control the mode as depicted by input from the mode switch an torque on demand relay an someother inputs . Probably has DTC - diagnostic trouble codes stored in the GEM module .
Transfer Case -Automatic Four-Wheel Drive (A4WD) The automatic 4-wheel drive transfer case system consists of the following:

• automatic 4WD indicator light
• brake pedal position (BPP) switch
• torque on demand (TOD) relay
• front output shaft speed sensor
• generic electronic module (GEM)
• 4WD high indicator light
• 4WD low indicator light
• 4WD mode switch
• rear output shaft speed sensor
• shift position sensor
• throttle position output (TPO) from the powertrain control module (PCM)
• transmission range sensor P1804 Transmission 4-Wheel Drive High Indicator Circuit Failure GEM REFER to Section 413-01 . P1806 Transmission 4-Wheel Drive High Indicator Short Circuit to Battery GEM REFER to Section 413-01 . P1812 Transmission 4-Wheel Drive Mode Select Circuit Failure GEM REFER to the Symptom Chart. P1815 Transmission 4-Wheel Drive Mode Select Short Circuit to Ground GEM GO to Pinpoint Test C . P1820 Transmission Transfer Case Clockwise Shift Relay Coil Circuit Failure GEM GO to Pinpoint Test B . P1822 Transmission Transfer Case Clockwise Shift Relay Coil Short Circuit to Battery GEM GO to Pinpoint Test B . P1824 Transmission 4-Wheel Drive Clutch Relay Circuit Failure GEM GO to Pinpoint Test A . P1826 Transmission 4-Wheel Drive Low Clutch Relay Circuit to Battery GEM GO to Pinpoint Test A . P1828 Transmission Transfer Case Counter Clockwise Shift Relay Coil Circuit Failure GEM GO to Pinpoint Test B . P1830 Transmission Transfer Case Counter Clockwise Shift Relay Coil Short Circuit to Battery GEM GO to Pinpoint Test B . P1836 Transmission Transfer Case Front Shaft Speed Sensor Circuit Failure GEM GO to Pinpoint Test A . P1837 Transmission Transfer Case Rear Shaft Speed Sensor Circuit Failure GEM GO to Pinpoint Test A . P1838 Transmission Transfer Case Shift Motor Circuit Failure GEM REFER to the Symptom Chart. P1846 Transmission Transfer Case Contact Plate 'A' Circuit Failure GEM REFER to the Symptom Chart. P1850 Transmission Transfer Case Contact Plate 'B' Circuit Failure GEM REFER to the Symptom Chart. P1854 Transmission Transfer Case Contact Plate 'C' Circuit Failure GEM REFER to the Symptom Chart. P1858 Transmission Transfer Case Contact Plate 'D' Circuit Failure GEM REFER to the Symptom Chart. P1866 Transmission Transfer Case System Concern - Servicing Required GEM REFER to the Symptom Chart. P1867 Transmission Transfer Case Contact Plate General Circuit Failure GEM REFER to the Symptom Chart. P1874 Transmission Automatic Hall Effect Sensor Power Circuit Failure GEM GO to Pinpoint Test A . P1875 Transmission Automatic Hall Effect Sensor Power Circuit Short to Battery GEM REFER to the Symptom Chart. P1891 Transmission Transfer Case Contact Plate Ground Return Open Circuit GEM REFER to the Symptom Chart. P1892 Trans. Automatic 4-Wheel Drive 4X4 Mechanical Lock Output Circuit Failure GEM GO to Pinpoint Test B . P1893 Trans. Auto. 4-Wheel Drive 4X4 Mechanical Lock Output Short to Battery GEM GO to Pinpoint Test B .
• Your best bet , take it to a qualified repair shop .

What trans? AOD? This is 1992 F Series, all I have.

Shift Controls, Automatic Transmission The transmission shift control linkage or cable transfers the transmission operating mode from the selector lever to the transmission. The indicated transmission position on the steering column is transferred to a shift lever on the bottom of the steering column. On vehicles equipped with cable-operated shift systems, the indicated position of the transmission selector lever is transferred to the transmission through the shift cane, then to the cable, and down to the transmission manual shift lever at the transmission. On vehicles equipped with shift rod assemblies, the rod transfers the indicated transmission selector level position through a bell crank assembly to a control rod. The control rod transfers the indicated position to the transmission assembly.
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Automatic Transmission Manual Linkage Adjustments

1. With the engine stopped and the parking brake applied, place the transmission selector lever at the steering column in the D (DRIVE position) for C6 applications and in the (D) (OVERDRIVE position) for AOD and E4OD applications, and hold against the D or (D) stop by applying a three-pound force to the selector lever knob.

1. Loosen the shift rod adjusting nut at point A. Refer to the following illustrations.

1. Shift the manual lever at the transmission into the (D) (overdrive) position for E4OD, by moving the lever all the way rearward, then forward two detents.

1. With the selector lever and transmission manual lever in the(D) position, tighten the nut at point A to 17-24 Nm (12-18 ft-lb) torque. Use care to prevent motion between the stud and rod.

1. Remove the three-pound force from the steering column selector lever knob.

1. Operate the shift lever in all positions to make certain that the manual lever at the transmission is in full detent in all gear ranges. Re-adjust the linkage if required.

1. On F-Super Duty Chassis Cab and Motorhome and Commercial Chassis recheck for correct operation of the automatic transmission selector indicator (PRN(D)21). Refer to Section 11-04A, Steering Column, Shift Rod Within Tube. CAUTION: Under no circumstances will it be permissible to adjust linkage in any position other than the(D) position for E4OD applications.
   

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Automatic Transmission Shift Cable Adjustment

1. From inside the vehicle, place the column shift select lever in the DRIVE position (C6) of the OVERDRIVE (AOD and E4OD). Hang a three-pound weight on the selector lever.

1. Raise vehicle on a hoist.

1. Remove the shift cable from the transmission lever ball stud.

1. Pull down the lock tab on the shift cable body.

1. Position the transmission shift lever in the DRIVE position (C6) or the OVERDRIVE position (AOD and E4OD). This is three detents from the front-most lever position with the first position counting as one.

1. Connect the cable end fitting to the transmission lever ball stud.

1. Push up on the lock tab to lock the cable in the correctly adjusted position.

1. Lower vehicle down from hoist and remove the three-pound weight from the column shift select lever.

1. After making the adjustment, check for park engagement. Check the transmission control lever in all detent positions with the engine running to make sure correct detent/transmission actions. Readjust if necessary.

Instructions vary depending upon if its a stick or automatic transmission. Your best bet if you haven't ever done anything like that is to get yourself a chilton or haynes manual. Both have text and pictures to help with the job. With hanynes, you may need the transmission manual instead of the regular repair one if its an automatic...check the contents before you buy it.
When doing an automatic, it's advisable to remove the crank sensor from the bellhousing as often they get damaged accidentally when working in there. If you need to remove the flywheel, make sure you mark it's position so you can put it back exactly the same way it was installed.
Make sure you have a flat solid area to work on. Transmissions need to be supported so notheing get's damaged. To do that, you need a place where you can move a jack easily. If you need to work on dirt etc, buy a sheet of 5/8" plywood to put underneath.

Thee is a mechanical tightening mechanism that goes over the rod that connects your shift lever to the PTO lever. It is secured with a bolt. If this bolt has come loose, the mechanism may have moved (slipped on the shaft) and the shift lever will not be synchronized with the PTO lever. There may be evidence this slippage on the rod. If so move it back to its original position and tighten. If not adjust in the direction you suspect it moved from in small increments until it works again. May need to reverse direction, of course, if it gets worse. Let me know if this helps. Thanks.

Ford has 2 types of 4x4 system engagement. One is a knob on the dash that you just turn to 4wheel drive high or low. The other system is the 4x4 transfer case shift on the transmission tunnel (hump) between the driver and passenger seats. To shift into 4 wheel drive high while driving, just let off the gas and shift transfer case into 4H position, and continue driving. To shift into 4 wheel drive Low, stop the vehicle completely, put transmission in neutral, shift transfer case into 4Low position, put trans. in gear, and start driving. I am assuming before doing the above, you have locked in ( turned the front hubs to 4 wheel drive position.) Any further questions, let me know.

Either your linkage is not properly adjusted or the shift fork is a bit worn inside the transfer case. I have a bit of wear on my own and shift into low range while rolling with no load, between 5&20mph and it works fine except that I need to anticipate needing it before hand. One important rule...If it grinds, don't force it into gear. That will cause damage.
Also, if you just got it, change the oil in there...you have no idea when it was last serviced.

the next time you shift into 4 wheel drive, try backing up alittle bit and see if it shifts in and light comes on. i have a 1995 half ton chevy pickup and thats what i have to do do to get it to lock in.