F 250 4WD Super Duty V10-6.8L (2002)
Wheel Hub (Locking): Description and Operation
For additional information regarding this component, please refer Transfer Case/Description and Operation. See: Transmission and Drivetrain/Transfer
Case/Description and Operation/Four Wheel Drive (4WD) Systems
Hublock Operation
The 4X4 ESOF system uses timed vacuum sequences to lock and unlock the wheel ends. A high vacuum level is used to engage the hublocks, and a
lower vacuum level is used to disengage the hublocks, after which the vacuum is released and the hublock holds itself in the proper mode. The vacuum
signals are supplied to the hublocks by system components, including the 4WD control module, wiring harness, solenoid, vacuum harness and vacuum
seals. As the first step in service, eliminate such obvious items as loose wiring connecting, loose vacuum connections, or damaged vacuum lines.
Disengage Time
"Slow" release of the hublocks is not considered abnormal for this system. Anytime vacuum is applied to the hubs, whether for 4X4 or 4X2, the
hublocks will initially engage. If 4X4 was requested, the hublocks will remain engaged, but if 4X2 was selected, the internal mechanism will release
only after the 4WD control module timers expire and vacuum is vented from the hub. This normally takes 15 seconds, but can take up to two minutes,
depending on how the 4X4 mode select switch was operated. After the hub mechanism releases, internal springs must work the hublock gears to the
disengaged position. Road bumps, vehicle speed, acceleration cycles, or momentary reversal of direction can assist this process, varying the length of
time the hublocks remain engaged in each situation.
Manual Override
The hublocks have manual override selector dials, which, when rotated to the "LOCK" position, will keep the mechanism locked regardless of the
instrument panel 4X4 mode select switch position. Verify that both dials are in "AUTO" before evaluating ESOF operation.
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. 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 proper operation of the ESOF hubs. Before diagnosing the hublocks themselves as the cause of 4X4
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, as 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.
