Routine Drivetrain Maint - Now 4x4 Not Working?

[cghoerichs]

I recently changed to Warn hubs because one was stuck in lock. Changed them out no problem. All was well and 4x4 was working fine. BUT I figured I'd change the transfer case fluid, front and rear diff fluid around the same time as the hubs which was a few weeks ago. Now my 4x4 isn't working. Coincidence?
1. My hubs are working - the drive shafts are locked when the hubs are Locked and rotate when Free
2. My transfer case is working - I can see the front drive shaft turning when in 4x4 (with back wheels sliding on a clay hill and front wheels not rotating).

Anybody know what to check in the front diff or anywhere else to make a diagnosis?

Additional info: No grinding noise when in 4x4 from the front diff or anything like that. Rear diff was 75/140 synthetic per tag. Front was standard lube (whatever the computer said at the parts place for 2002 7.3 F-250 4x4).

[NoRalPh]

No fluid change would stop it from working. If you're sure the TC is going into 4WD then you don't have your hubs locked.

Jack one side of the front of the truck up and spin the tire. THAT should answer all possibilities.....

In 4WD you shouldn't be able to turn either tire with the rears on the ground (one side in the air at a time). Lock & UnLock each hub to see the difference.

Also, if just One of the hubs is UnLocked the power will go to that "free" axle and the 4WD won't work.

[cghoerichs]

Here's more info:
Here is what I found:
2WD & HUBS LOCKED
Front axles are locked
Front drive shaft turns
2WD & HUBS UNLOCKED
Front axles turn
Front drive shaft turns
4WD & HUBS LOCKED
Front axles are locked
Front drive shaft locked
4WD & HUBS UNLOCKED
Front drive shaft locked
Front axles turn

[NoRalPh]

Originally Posted by cghoerichs

Here's more info:
Here is what I found:
4WD & HUBS LOCKED
Front axles are locked
Front drive shaft locked

Sounds like you've got 4WD to me

[cghoerichs]

One would think, but it appears that the diff isn't transferring the drive shaft power to the front axles.

[NoRalPh]

According to your description, your front wheel is connected, without slipping, to your crankshaft (or Park prawl in an Auto)

I don't know how it can be any other way.......

Test it again, I have a feeling you will find 4WD IS working

[cghoerichs]

I'll check again in a minute, but it really looks like the front diff isn't working. I was able to observe from outside of the truck while my son "drove". The truck was stuck on a clay hill. Back tires spinning, front drive shaft turning, front tires just sitting there. 4WD on and hubs locked. Did all of the test with everything in the above mentioned settings. The only thing I can figure is the front diff isn't working but it makes no noise when the front drive shaft is turning.

[NoRalPh]

If I had to Guess,,,, I'd bet one of your new hubs wasn't Locked that time!

[cghoerichs]

Nope. I just had to use my skidloader to pull the truck off of a clay spot. Hubs are in, checked both front axles they are locked when the hubs are locked. Drive shaft spinning when in 4WD.

[NoRalPh]

Geeeez I'm sorry,,,, I cannot "wrap my head" around this

If you try and turn a ft tire (either one), with the hub locked, in 2WD you see the Ft axle turning (try and hold it maybe to see if you can stop it?) AND when you put it in 4WD everything's locked - right?

BUT when you need the ft axle to help you off a slick spot, the rears spin, the driveshaft spins, the ft tires just sit there.....

Makes No Sense to me, if the ft diff was "skipping" there'd be bangin & clangin (plus you just changed the oil and, I assume, didn't see all kinds of metal or anything) I have to believe it's a hub problem more than the diff.

Just for S&Gs I'd be tempted to jack the rear up (both sides), put it in 4WD, and give it a little gas (DON'T GET UNDER IT!!!) to see what happens. Really ALL 4 wheels up (if you can do it) then you could look it over right! Maybe look at the ft U-Joints before the hubs for spinning without the wheel (nonlocked hub)

I donno,,,, you got a puzzler there!