I had the same problem on my truck. As far as I know the same exact system is used on all the f150 trucks starting in 2004 and an older version was used before that. It consists of a plastic gear ring air vacuum hoses, a solenoid and a rubber diaphragm. They are weak and prone to breaking especially when they get wet mine lasted 100,000 miles because it was not wheeled very hard before then. The raptor has the same system installed on it and as far as I know the only aftermarket solution is manual locking hubs which you need special rims for. The key to keeping them happy is staying out of water, deep mud and if you go into deep water or deep mud blowing them out with an air hose.
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