If you've pulled a vacuum on both lines from up on top at the canister, then most likely the seals in the hubs are shot. "Make sure you separate the two lines at the "T" and make sure you test from up on top". It's too expensive to replace the seals so I'd install the Warn 60247 manual hubs available on Amazon.com. Cost is $121 delivered including shipping. I just got a pair...took me 20 minutes to install...comes with all instructions.
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Most common problem is a vacuum leak to the hubs. Check the lines from the vacuum pulsating solenoid all the way down to each hub connection. If the lines are good,use a vacuum pump to apply vacuum to the hub with the line removed. You should hear a slight click at about 5 inches of vacuum if the hub seals are good(test both hubs individually). Just one bad seal in either hub can cause the entire system to malfunction.
Sounds like you have a vacuum leak. The pump will run continuously when its not building vacuum. The vacuum seals at the hubs are a common failure on those i would start there by disconnecting the lines right at the hub and applying vacuum directly to the sealed hub unit. I believe it should hold 15-20 in hg
The hubs on this vehicle are vacuum operated and controlled by a module and a solenoid valve. When there is no vacuum applied to the hubs they should be locked in. The hubs will unlock with vacuum applied. Disconnect the vacuum lines at the hubs and see if the axles freewheel. If they do you likely have a hub issue. If the hubs are locked in with the lines disconnected you probably have a faulty solenoid valve.
the vacuum hoses or wheel seals are leaking in the front wheels. they are vacuum operated. the dealer has kits you can buy to convert to manuel locking hubs, they had alot of problems with the vacuum hubs
There are issues with the 4x4 system I.w.e ends ingesting moisture/water
into vacuum actuation system causing no 4x4 or ratcheting outboard I.w.e
ends. (Even if you don't go 4x4'n ) pull off vacuum hoses @ I.w.e ends
and check for moisture/water/rust also the I.w.e is not part of the
wheel bearing itself It is the part on the axle side (inboard) of the
spindle. (EVEN DEALERS CAT LISTED WRONG)Many shops just replace the
wheel bearing side this may fix the symptom but not the true cause of
damaged I.w.e. ! Check with a reputable dealer they should have info on this condition and repair procedure.
The integrated wheel end (IWE) system contains the following:
Vacuum reservoir IWE solenoid IWEs (spring loaded vacuum hubs) Vacuum hoses Check valve The
IWE system uses vacuum hubs that engage the front wheel hubs to
the front half shafts or disengage the front wheel hubs from the
front half shafts.
The IWE solenoid receives engine vacuum from the vacuum reservoir.
the 4-wheel drive system is in 2WD mode, the 4x4 module (PCM)supplies a
ground path to the IWE solenoid to apply vacuum to the integrated wheel
ends (disengaging the front hubs from the front half-shafts). In 4WD
mode, the 4x4 module (PCM) does not supply the ground path to the IWE
solenoid, vacuum is not applied to the integrated wheel ends and an
internal spring keeps the front hubs engaged to the front half-shafts.
luck and check the vacuum line, start with the simple.
Keep me posted, be glad to get your 4wd working again and rate please.
The light comes on indicating that the transfer case is engaged in 4wd, but that doesn't mean the hubs are locked. If you have automatic locking hubs, you should check to make sure they are working correctly. This GM vehicle may be equipped with vacuum locking hubs... meaning there is a vacuum line running from the transfer case selector to the hubs on each side. The vacuum makes the hubs lock into place. If those vacuum lines are damaged or missing, they wont lock. If you have electronic locking hubs, they may need to be replaced. Good luck.
the hubs on that truck are a vaccum controled hub, when the swithch is turned to 4x4 the vaccum control solenoid (on the fender) applys vaccum to the hub and locks- you can put a vaccum gauge on the hubs- if a leak is found thre is an o ring and an axle hub seal that needs to be replaced... if no leak is found at the hubs check the vac. lines and solenoid.goodluck
They are operated by vacuum. Check to make sure the vacuum lines are connected and not ripped or anything. If that checks out fine, remove the vacuum line from the hub and apply vacuum to the hub, if the hubs lock then the problem is in the vacuum line or switch.
The rubber vacuum hose comes off the intake manifold inside the engine compartment. The vacuum lines are located on left side fender, under the hood. If you look facing motor you will see tehm on the right side.