Hublock Replacement

Left- and right-side hublocks are not connected, other than by the common vacuum supply line. If a malfunction in either hublock is diagnosed, it should be installed as an individual unit; there is no need to "balance" an axle with new hublocks on both sides. It is highly unlikely that both hublocks 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 hublocks on both sides.

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

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

Electronic Shift Vacuum Schematic 

Feature Inputs: 

• Mode select switch (MSS)
• Vehicle speed (hardwired to 4x4 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 hublock (PVH) solenoid assembly
• PVH vacuum pump (certain diesel applications only)
• Cluster indicators (hardwired to instrument cluster via 4x4 module)

During 4x4 Initialization at Startup: 

• The 4x4 module will verify the MSS position
• If the transfer case is not in the desired mode, the 4x4 module will attempt to perform a range shift. If input conditions for 4L are not present, then the module will either shift to or remain in 4H
• 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 2H, 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 2H to 4H or 4L, the Following Sequence Occurs: 

• MSS is switched from 2H to 4H or 4L
• For shift attempts into 4L:
  • 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 (2H to 4H or 4H to 4L) totaling 5 clockwise movements and 5 counterclockwise movements with an approximate 1-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 C1728 (for 2H to 4H attempts) or DTC C1729 (for 4H to 4L 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 reattempt 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" and (if 4L) "Low Range" lamp will illuminate. This ONLY occurs when the driveshafts are synchronized. If they are not, then the "4x4" lamp will not illuminate
• Once the 4x4 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 2H)
• 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 4L to 4H to 2H, the Following Sequence Occurs: 

• 4x4 mode select switch is placed from 4H or 4L to 2H
• For shift attempts out of 4L:
  • 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 disengages dual-cone synchronizers
• If a blocked shift condition occurs, the shift motor will perform 10 shift attempts from 4H or 4L to 2H to 4H or 4L to 2H totaling 5 clockwise movements and 5 counterclockwise movements with an approximate 1-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 2H and 4H) or DTC 5729 (for attempts between 4H and 4L) 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 reattempt a shift (4H to 2H 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", and if 4L, "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 4H or 4L, 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 4H or 4L