I’ve got a 2001 7.3 (232,000 miles), and I’ve got a little issue with the four wheel drive. Found out it didn’t work because I got it stuck turkey hunting this morning. ESOF switch in the cab works, both “4x4” and “Low Range” both light up on the dash display, the transfer case engages because I can hear it lock in and the truck lurches forward when put into low, Vaccum works fine because the AC loses its air speed and switches to the defroster position whenever I turn the switch. Tried locking the hubs and still no luck. Looked at a bunch of other forums and nobodies symptoms quite match mine. I believe it’s a vacuum leak, but I’m tight on money at the moment and I don’t want to go tearing into it and fix something that doesn’t need fixed. Need a little direction as to where to start on it. Please help!

 

Even if you lost the vacuum, manually locking the hubs would override that.

You say that you hear the transfer case engaging and think that is working.

Assuming it’s not still stuck in the mud, try engaging the 4wd now and see if it works.

If it doesn’t, you can check to see if the front axles are locking by manually locking the hubs and putting it in 4wd. Then reach doen and manually try to turn each front axle. If you can turn them by hand, then the transfer case is not engaging.

 

^^^^ Great advice to see mentioning turning front ujoints by hand. Even tho i have manual hubs and transfer case i always do those steps every time i go in or out of 4x4, even after i dont lock the hubs, but just use 4wheel low to achieve 2Low.

To share a phrase we use often at my work; Trust but verify

 

If the vents goe into defrost when you put it in 4x4 then everything isn't working fine, that means you have a vacuum leak. However locking the hubs manually bypasses the vacuum, you may have a bad hub.

 

If the hubs are locked you won't be able to turn the axles even with the transfer case in 2wd.

 

I just figured the lack of AC coming from the vents was an indicator the vacuum was getting the 4x4 engaged. Good to know because that may be the root of the whole problem.

 

yes you can. I know because when swapping tires, I have to engage the 4wd to keep the fronts front spinning if they’re off the ground when I’m doing the lug nuts

that’s also why you can leave your hubs locked all winter but not have the transfer case engaged

 

I think that with the hubs locked it would be pretty difficult to just grab an axle and spin it because of the resistance from the differential and the transfer case but they would still spin with a lot of oomph.

Is the truck new to you and your just discovering this, or is it your working truck that this just happened on? As stated above, with the hubs locked manually they should work. If they're not you need to jack up the front end and start troubleshooting and I'd start at the hub with the wheels on, hubs locked you should see an increase in resistance for turning the wheel and the axles should spin (do this with the dash switch in 2X).

 

If the tires are on the ground you can't turn the axles by hand with the hubs locked because you would be trying to turn the wheel, if the tire is off of the ground you can but the wheel will turn with it.

 

you are correct; wasn’t thinking if that. Too many variables early in the morning......

 

Had the truck since October 2017. Daily driver to and from work and hunting trips on the weekends. Bought it from what seemed like a straight up dude. Told us it was pristine, got it home and discovered it needed a whole lot of engine related stuff. Of course it was a 16 year old truck when I got it so I was expecting to do some work on it but wasn’t expecting to do that stuff. Told us it wasn’t tuned or chipped but it rolled coal obnoxiously getting on the highway so I went and had the computer reset. It was bad on my part because I just took his word for it and didn’t really go digging through it, and I’ve drove Powerstrokes all my life and worked on 7.3’s and 6.0’s at my dads shop so I figured I knew a good truck when I seen one and drove it, guess I’m not as good as I thought lol. So I’m just assuming that this has been a problem with this truck for a while now, given all the other stuff I had to do to it. I hate that I buried it in a muddy mess to figure out the 4x4 didn’t work. Got it stuck so bad, my five year old son (first time I took him turkey hunting by the way) said “Are we gonna have to leave your truck here forever dad?” Anyways, didn’t mean to go on such a huge spill but I thought I’d share what I’ve dealt with.

 

Probably most of the folks on here have been stuck in the mud at some point, when the 4x4 refused to engage. That big heavy diesel doesnt like mud in 2-wheel. Before hunting season, I always pull my hubs, clean them, etc.... and make sure 4x4 works before going to the National Forest. Its a LONG damn walk back to my house from the woods.

If its "rolling coal ", I'd put in injector o-rings for less than $50, unless you're going for new injectors.

 

OK, so you don't know if it's a new problem or one that's been around for a while. It sounds like first you need to hose the mud off of it.
Then start as described above and trouble shoot. Manually lock the hubs and see where the failure is.

 

IS there a front drive shaft? Silly question, but with locking the hubs and the transfer case sound like it is engaging that link between them may be missing?

 

My guess is that the 4wd is working and you thought it wasn't just because it got stuck. Maybe the driver's front wasn't spinning, but the passenger side one may have been. Without a differential locker it's very common to only see one spin when you're in slippery stuff. If you know for an absolute fact that neither one was spinning then there's a problem. It's also possible that the hubs were locked and you unlocked them, been there seen that. Clockwise to lock, counter-clock to unlock. Kinda like righty tighty lefty loosey when dealing with a screw.

If you raise all 4 wheels you can verify if the fronts are getting power by engaging the 4wd, putting it in gear, and letting off the brakes. Alternatively, raise one front and lock that hub, rotate the tire and you should see the front driveshaft rotate. Then engage the transfer case to 4wd high or low and that tire should no longer freely spin because the T-case locks the front driveshaft and rear driveshaft together. Then do the same with the other front tire.

The fact that your vents changed indicates a weak vacuum pump or a leak in the hub engagement system, regardless, once the hubs are manually locked the vacuum has no effect on 4wd performance.