Join Date: Sep 2008
Location: Oakbank, Manitoba
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The tubes attach to the back of the front hubs. You might be able to see the deterioration of the hoses, but it could be anywhere back up to and including the vacuum pump. To check the hubs you need to hook up a vacuum source and see if it bleeds off. Of course, there may be other causes like wiring or switches.
With the hublocks in the AUTO position, the 4WD ESOF system uses timed vacuum sequences to lock and unlock the wheel ends when switching the
instrument panel MSS between 2WD and 4x4 modes. A high vacuum level (222 mm [8.75 in] Hg and greater) is applied to the hublocks to lock the internal spring mechanism that engages (locks) the hublocks for 4x4 mode, and a lower vacuum level (114 to 184 mm [5.9 to 7.1 in] Hg) is applied to unlock the
spring mechanism that disengages (unlocks) the hublocks for 2WD mode. The vacuum signals are supplied to the hublocks by system components, including
the 4X4 control module, wiring harness, solenoid, vacuum harness and vacuum seals. As a first step in service, eliminate obvious items such as loose wiring
connections, loose vacuum connections or damaged vacuum lines.
This where I would start with your problem. To see how it all works, raise the front axle off the ground and run vacuum checks to lock and unlock your hubs.