So I have a 2003 F350 SD 4x4 Quad Cab LB DRW truck. It is equipped with front hubs marked Auto and Locked. I run primarily in the Auto setting. When I turn the 4x4 switch in the cab I cannot feel the truck go into 4x4. I don't get the normal dry pavement turn issue as I get in Locked 4x4.
I would assume that the Auto would be unlocked for better fuel economy and when I put it in 4x4 it will shift to that mode. Am I wrong? Do I have a problem? Or does Auto mean that if the system senses the rear wheels slipping that it will engage the 4x4 like some other systems.
When in the Locked position it seams to work fine, except doesn't matter if the switch in the cab is in 4x4 or not, I get a degree of the dry pavement noise from the differential when turning.
Can't find anything in the owners manual that I down loaded from the internet. Your help would be greatly appreciated.

 

You are right auto the hubs should be unlocked when the truck is in 2wd when you switch to 4x4 it uses vaccum to lock the hubs. Nothing in the front end should be spinning when the hubs are in auto and the truck is in 2wd. Unfortunately the factory hubs suck and usually have leaks somewhere in the system so they don't work right it's very common to replace the hubs with manual hubs and cap off the vaccum system or they get frozen where you either can't turn them or they are very hard to turn. The easiest way to tell is when in 2wd reach under the truck and try to spin the front driveshaft it should spin freely with hubs in auto and truck in 2wd then you can switch to 4x4 and leave the hubs in auto and the drive shaft shouldn't free spin anymore.

 

So what is the difference between auto and lock?
When the hubs are in the Auto position, does that mean all the gear is free and not turning until you move the switch then vacuum shifts the hubs into the lock position and the transmission provides the power to turn the gear?
When the hubs are in the Locked position, does that mean all the gear is turning from the wheels back but just no power from the transmission unless the switch is in 4x4?

 

https://www.ford-trucks.com/forums/1...em-please.html

 

Thanks, that helps a lot. I guess I need to check into the auto function. Probably a vacuum issue as I think the vacuum only operates in the Auto mode.

Assume to start with the vacuum tubes to the hubs and then the relay for the vacuum system and finally the vacuum pump.