I have a 2004 F-150 5.4L (160,000 miles) with a problem with its 4 wheel drive. I recently replaced both bearings and actuators on the front end with OEM parts, but recently I have discovered that the vacuums that engage and disengage the 4 wheel drive will not turn off causing the truck to stay in 2 wheel - this has been a problem even before parts were replaced. When the tubes that are connected to the bearing/actuator are removed the 4x4 kicks on. Any information on this problem would be greatly appreciated.

 

There are some vacuum valves that get wet and then need to be replaced. I believe they are on the firewall on the passenger side.

 

Yes on the passenger side fire wall. Looks like this.

 

Thanks everyone