I own a 2005 Ford F-150 SuperCab 5.4 Liter, four-wheel-drive with 42,000 miles on it. The four-wheel-drive went out and I came to find that the IWE solenoid and hubs were bad. The IWE solenoid went bad causing the hubs to not stay fully disengaged destroying them as well.
It was fixed at the local Ford dealership, and what strikes me as odd is that the new IWE solenoid has a rain guard over it. Seems to me that when they have a problem like this it should be considered for a recall, and the consumer should not have to pay for a faulty design. I contacted Ford and they said it was not a malfunction.
As a matter of fact, Ford Technical Service Bulletin number 06-8-15 deals with a similar condition -- water intrusion of the IWE (Integrated Wheel Ends) solenoid. The symptoms described in the service bulletin differ a little from yours, but it sure sounds relevant.
The described problem involves water intrusion through the IWE solenoid contaminating the rest of the vacuum actuated system, and causing noise while in two-wheel drive. There's also potential for the solenoid to short circuit, set trouble codes C1979 and C1980, and disable the 4WDH light.
The IWE solenoid normally applies vacuum to the Integrated Wheel Ends (locking hubs), and disengages the hubs while in two-wheel. In four-wheel, the powertrain control module commands the solenoid on, cutting off the vacuum supply and therefore engaging the spring loaded hubs.
It seems as though the water contamination can obstruct the flow of vacuum and lock (or partially lock) the hubs while in two-wheel drive, which may damage the splines on the hubs and/or CV joints.
The fix is to clear the vacuum lines of water, and replace the IWE solenoid with a modified unit which includes a bracket to shield the solenoid from future water intrusion.
This is a technical service bulletin, not a recall. It even stipulates that the condition is only "eligible under provisions of new vehicle limited warranty coverage". You're best case is show the TSB to the Ford dealer service manager and politely ask for restitution, seeing it is a known problem requiring a modified part to correct. He may be able to send it through under warranty with an OK from the Ford zone representative, or provide some kind of good faith discount. Being a previous cash-paying service customer wouldn't hurt.