Auto 4x4 hubs how do they work?

[Thecat]

2004 F250 Harley Diesel 4x4 electronic 4x4 I can switch the selector to 4x4 and my trucks not locking into 4x4 everything is spinning out to the Hub but they seem not to be locking in. I've taken them apart and they look like new. Any Ideas how these auto hubs work? What could my problem be ?
Thanks for any help..

 

[MBRPCrazyford]

If I'm correct, they work off of vaccum. you could have a vaccum leak somewhere.

 

[keanoknick]

You could very likely have a vaccum leak. Does your climate control work ok, or is it stuck in the defrost position. if it's stuck in defrost, you definantley have a vaccum problem. Also check your relay

Also you can manually lock your hubs by rotating the knob on each one to the "lock" position.

 

[slopony]

As he said above about the vaccum. There is a pump cause we dont make vaccum and i know they were know to go out don't know where it is on the 6.0 would check but the 6.0 is'nt here. It looks like a really easy fix to replace the pump if thats the problem would'nt take any more then 10 minutes. You can try unpluging the pump then plugging it back in and it might work for a while but prolly not hat long. Best way to check if its working is if just your defrost works. sorry about the babbling

 

[Kleetus]

Go for the easy ones... check your hose connections on the back side of the spindle and where it connects at the frame. Go for the simple and obvious stuff first.