I have a 2008 F-250 Superduty 4x4 (60,200 miles, just over warranty).

I sometimes think that my truck is in four wheel drive if I put the truck in reverse to turn around. The front wheels feel like they are grabbing when I do this sometimes.

I had a friend pull the truck forward and back and I noticed that sometimes the hub U-joints and drive shaft for the 4x4 turn even though the switch is not in HI or LOW.

I don't notice the "jerking" of the front end when I turn in a circle in a parking lot when this happens so I tend to think that the 4x4 is not engaged. When I do turn the switch to 4x4 HI, the truck jerks when I turn, so I know it is engaged.

Is it possible that somehow there may be a vacuum issue that is causing the hubs to turn, but not engage sometimes? I did have to replace the vacuum hose last year because the line got melted from the hole in the battery compartment caused some acid to drip on it and the solenoid just ran all the time because of the hole.

The dealer said he thinks it may be the vacuum solenoid is going bad, but I would have to take it in to have them look at it.

Looking to see if I can't get some advice before I take it in. Why would the 4x4 drive shaft/hubs turn sometimes when the switch is not in 4x4?

Thanks for your time and if I haven't confused you enough, ask me a question so I can clear up my rant.

 

Are your hubs locked?

 

Agreed, sounds like your hubs are locked. If the hubs are locked, then the wheels are turning the axle shafts, diff, and driveshaft. Since the transfer case isn't engaging 4x4, then there's no tension against the front wheels in a turn so you won't feel it bind up like it normally would. Best way to check hubs I believe is to jack up the front end, and turn a wheel. If the ujoint moves, the hub is locked. Could use a cleaning or a replacement to manual hubs - the factory vacuum hubs are known for going bad - had to replace mine at 125k on the excursion.

 

I will have to check it when I get home, but I would have to assume they are NOT since the ujoint and drive shaft do not always turn.

Last year when I took it in to the dealer for oil change, they said that one side was locked. I had just got new tires the day before and the mechanic said the tire place must have locked one side on accident.

Sounds odd, but would there be any way the manual hubs can lock themselves? They are covered by my rims so I would have to take off the tire to see.

 

If you have truly manual hubs, then no. If you have Ford's automatic hubs with the manual **** (set to 'auto'), then I suspect they occasionally fail to unlock.

Mine (on 2 diff trucks) would erratically fail to unlock and I was tired of cleaning and lubing and fiddling, so I installed manual hubs. More work, but I know positively that I'm not taking a 300 mile trip on a summer day with one hub still locked.

 

The common culprit is the hubs, locked or unlocked. After a while they will get stuck. This happens because moving parts move, and eventually get stuck and need new lubrication. Thats life. So what you have to do is do your AutoHub maintenance. Thats what fixed it on mine.

Follow these instructions on hub lubrication.
Welcome to guzzle's 4x4 Autolock Hub Lubrication Maintenance Web Page

Here is a perfect video of what you are describing. This is on my truck.

4x4 Front Driveshaft (Hubs Stuck) - F250 7.3L Powerstroke - YouTube

 

Thanks for the link. I will order the kit and will do the service on the hubs and let you all know if it solves the problem. Sounds like I need to do this anyway so it can't hurt.

 

After I did mine, my 4x4 system operated so much smoother.

 

i have seen trucks drive down the highway with the front driveshaft kind of lazily spinning at about 30-50 rpm but that is clearly just from the fluid moving around i guess

 

That's normal. Even when the hubs are unlocked there is still a small amount of friction and that causes the slow rotating.

 

dude your brake line shouldn't be rubbing on your shock's like that.

 

dude, it's not.

That's my hub vacuum line. When I replaced it it got cut too long