Hub lock Replacement

LH- and RH-side hub locks are not connected, other than by the common vacuum supply line. If a malfunction in either hub lock is diagnosed, it should be installed as an individual unit; there is no need to "balance" an axle with new hub locks on both sides. It is highly unlikely that both hub locks are malfunctioning at the same time on a vehicle. If both sides appear to be malfunctioning, be sure to verify upstream integrity before installing new hub locks on both sides.

Many system components are involved in the correct operation of the ESOF hubs. Before diagnosing the hub locks themselves as the cause of 4WD concerns, be sure to verify all related system components.

After removing the hub lock retaining ring, be sure not to use tools other than hands or "grip" gloves to remove the hub lock. Damage may occur to either the paint or the function of the hub lock. Pliers or locking Channel-Locks® should be considered as a last resort, and will usually damage the hub lock, making it necessary to install a new hub lock. Carefully shake the U-joint while attempting to remove the hub lock; this should reduce hub lock-to-axle shaft spline friction and ease removal.

Fig 1: Electronic Shift Vacuum Schematic

Courtesy of FORD MOTOR CO.

Feature inputs: 

• Mode select switch (MSS)
• Vehicle speed (hardwired to 4X4 control module via ABS)
• Encoder position inputs A, B, C or D
• Transmission NEUTRAL position (automatic transmission)
• Clutch apply signal (manual transmission)
• Brake ON/OFF (BOO - hardwired from brake pedal switch)

Feature outputs: 

• Transfer case dual-cone synchronization clutch
• Transfer case shift motor and Hall effect encoder assembly
• Transfer case shift motor relays
• Pulse vacuum hub lock (PVH) solenoid assembly
• PVH vacuum pump (certain diesel applications only)
• Cluster indicators are controlled by the IC which interprets outputs from the 4X4 control module

During 4WD initialization at startup: 

• The 4X4 control module will verify the MSS position
• If the transfer case is not in the desired mode, the 4X4 control module will attempt to carry out a range shift. If input conditions for 4X4 Low are not present, then the module will either shift to or remain in 4X4 High
• Once the transfer case is engaged, or is already in the correct mode, the PVH lock/unlock and/or lock solenoids will be energized
• If the MSS position is 2WD, the PVH lock/unlock solenoid will be commanded to energize ONLY at speeds below 8 km/h (5 mph). Once this speed threshold is met, the solenoid will be de-energized. This procedure is to prevent ratcheting induced by an attempt to unlock an already unlocked hub

For a shift attempt from 2WD to 4X4 High or 4X4 Low, the following sequence occurs: 

• MSS is switched from 2WD to 4X4 High or 4X4 Low
• For shift attempts into 4X4 Low:
  • the brake must be applied.
  • transmission must be in NEUTRAL (or clutch pedal applied).
  • vehicle speed must be below 8 km/h (5 mph).
• Shift motor moves range fork in transfer case, which engages dual-cone synchronizers
• If a blocked shift condition occurs, the shift motor will perform 10 shift attempts (2WD to 4X4 High or 4X4 High to 4X4 Low) totaling 5 clockwise movements and 5 counterclockwise movements with an approximate one-second delay between each motor movement attempt
• If, after 10 attempts, a shift is not completed, then the module will command a shift motor rest time of 40 seconds, before it attempts any further shifts
• After the 40 seconds have expired, the motor will make 10 more attempts to complete the shift. The motor will continue to repeat this sequence a total of 6 times (60 shift attempts) before ceasing operation. No further shift attempts will be made, nor will any further MSS commands be recognized. The vehicle must be restarted for 4WD function to be restored. If this occurs, DTC C1728 (for 2WD to 4X4 High attempts) or DTC C1729 (for 4X4 High to 4X4 Low shift attempts) will be stored in memory
• If the vehicle is driven above 5 km/h (3 mph) during a 40-second rest period, the module will re-attempt the shift strategy outlined previously. Generally, the transfer case will engage as the probability of gear teeth blockage is greatly reduced while rolling
• If no gear teeth blockage is present, the transfer case synchronizers bring the front driveshaft to same speed as rear driveshaft
• Shift fork completes movement and the 4X4 High and (if 4X4 Low) "low range" lamp will illuminate. This ONLY occurs when the driveshaft are synchronized. If they are not, then the 4X4 High or 4X4 Low lamp will not illuminate
• Once the 4X4 High or 4X4 Low lamp is illuminated, the PVH lock and lock/unlock solenoids are energized for 45 seconds, with approximately 62 kPa (9 psi) of vacuum or more at the hubs. The PVH lock sequence cannot be overridden at any time (a mode shift change back to 2WD)
• After 45 seconds have elapsed, the solenoids undergo a 6-second vent period, whereby no commands to either the lock or lock/unlock solenoids are allowed, regardless of MSS position
• If the vehicle is driven above 8 km/h (5 mph) the PVH lock and lock/unlock solenoids are re-energized in the same manner, regardless of whether the hubs are engaged or the original 45-second engagement timer has expired

For a shift attempt from 4X4 Low or 4X4 High to 2WD, the following sequence occurs: 

• MSS is placed from 4X4 High or 4X4 Low to 2WD
• For shift attempts out of 4X4 Low:
  • the brake must be applied.
  • transmission must be in NEUTRAL (or clutch pedal applied).
  • vehicle speed must be below 5 km/h (3 mph).
• Shift motor moves range fork in transfer case, which disengages dual-cone synchronizers
• If a blocked shift condition occurs, the shift motor will carry out 10 shift attempts from 4X4 High or 4X4 Low to 2WD to 4X4 High or 4X4 Low to 2WD totaling 5 clockwise movements and 5 counterclockwise movements with an approximate one-second delay between each motor movement attempt
• If, after 10 attempts, a shift is not completed, then the module will command a shift motor rest time of 40 seconds, before it attempts any further shifts
• After the 40 seconds have expired, the motor will make 10 more attempts to complete the shift. The motor will continue to repeat this sequence a total of 6 times (60 shift attempts) before ceasing operation. No further shift attempts will be made, nor will any further MSS commands be recognized. The vehicle must be restarted for 4X4 function to be restored. If this occurs, DTC 5728 (for attempts between 2WD and 4X4 High) or DTC 5729 (for attempts between 4X4 High and 4X4 Low) will be stored in memory.
• If the vehicle is driven above 3 mph (5 km/h) during a 40-second rest period, the module will re-attempt a shift (4X4 High to 2WD only). Generally, the transfer case will disengage as the probability of torque trapping is lower while rolling
• If no torque trapping is present, the transfer case synchronizers decouple the front driveshaft
• Shift fork completes movement and de-energizes 4X4 High, and if 4X4 Low, "low range" lamps. Once the 4X4 lamp is de-energized, the PVH lock/unlock solenoid is energized for 15 seconds, pulling approximately 41 kPa (6 psi) of vacuum at the hubs
• The PVH unlock sequence can be overridden at any time such as a mode shift change back to 4X4 High or 4X4 Low, relocking the hubs
• After 15 seconds, the solenoids undergo a 6-second vent period; the vent period can be overridden at any time by a shift attempt to 4X4 High or 4X4 Low