4WD Hubs

loadtoad

2011 Ford Expedition. 4WD system works, but in 2WD the hubs keep trying to engage when throttle is applied which obviously causes sounds nobody wants to hear. Have replaced the check valve in the vacuum line-no change, even turned it around in case it was backwards, no change. Any ideas?

thecardoc3

Ford's IWE "Integrated Wheel End" system hubs use vacuum to disengage the hubs, and turn the vacuum supply off to engage the hubs. The first thing to check is whether or not you have a full vacuum signal to the hubs. The best way to do that is to measure the engine vacuum to the solenoid, and then through the solenoid with the line to the hubs disconnected. Switching the 4WD system in and out of 4WD should cause the solenoid to block vacuum to the hubs (4WD) and allow vacuum to the hubs 2WD.

Once you know that the vacuum supply is correct and if the solenoid is operating correctly, then you need to prove whether or not the system has any leaks between the solenoid and the hubs. A hand vacuum pump works well for this, and you should be able to apply vacuum to the hubs, (including the lines to the hubs) get them to disengage and hold vacuum.

One last thing to check for is water in the vacuum lines. That can happen when there are leaks down in the hub assemblies.