I have a 99 F150 Lariet 4X4 with the switch on the dash for 4 wheel drive. It goes into 4X4 no problem, but will only come out if i back up a bit. Is this normal? It has the vacuum servo on the front differential. I've never owned one before, and don't have the owner's manual. I tried searching but couldn't find anything. Thanks! This board is awesome, has a lot of good info!

 

Thats how automatic hubs typically work.

 

Ummm...his '99 doesn't have locking hubs.

However, if you drive it too much in 4wd on a paved road or other good-traction surface, it is possible that you could get the entire driveline "in a bind", which could prevent the system from shifting back into 2wd until you release the "bind" or "tension" on the driveline by backing up.

Right off hand, I can't think of any other possbilities.

 

any vehicle with 4x4 has hubs. It just so happens that ours are automatic and are integrated with the bearings so you dont see them protruding from the wheel as you might older versions of the truck that had the manual hubs.
My 4x4 uses the floor shifter, so no electronic components, so you can shift it out of 4x4, but to truly disengage the hubs, you have to back up approximately 10-15 feet while 4x4 is disengaged. I'll have to check but I believe this is in the manual.

 

Sorry Matt, these 97+ trucks have a vacuum controlled center axle disconnect. Same system used on the Jeeps for a few years now. When you or I or anyone with a manual or ESOF transfer case ingage 4x4, the GEM computer uses a vacuum pulse to lock or unlock the axle. The axle is always spinning which is the reason for CV joints up front.

As with standard auto hubs, a center axle disconnect can be reversed to unlock instantly, or after awhile going forward.

Adrianspeeder

 

Edit: I'm such a slow typist, adrianspeeder beat me to the reply

Beg to differ. Ford F150s '97-'03 do not have auto-locking/unlocking hubs. The axle shafts are always turning when the vehicle is moving, whether or not 4wd is engaged. They have a Center Axle Disconnect (CAD), which keeps the front driveshaft from turning, but the left and right axle shafts are always turning on these trucks.

GM has used CAD since '87 or '88, and Dodge since '94.

I had thought Ford continued the CAD system to this day, but I was recently schooled on the subject. Beginning with the new '04s, Ford re-introduced what amounts to auto-locking hubs. They are a new style developed by Warn. They are called Integrated Wheel-End (IWE) disconnects, and they are vacuum-operated, not inertia locked, so no need to back up to disconnect.

Ford has not used "backing-up" style auto-locking hubs since the '96 model year.

 

well if two people correct me, I must be wrong .
I'm just curious as to why then, when you replace your bearings, you have to purchase a "bearing/hub unit". That's why replacing bearings costs you about $300 per side. Unless maybe thats integrated with the vacuum assist system you discussed.
This is the part I am referring to that is being removed in this picture (taken when I was installing my Skyjacker suspension lift):

There is definately more to it then jsut bearings and the chiltons manual described it as a bearing/hub assembly. Price quoted from Ford was approximately $275 for a new unit, per side.

 

I think in the technical sense, the term "hub" has nothing to do with whether or not it unlocks. Even a 2wd vehicle will have "hubs" in that sense. I guess it loosely refers to the spindle and bearing assembly. Remember when vehicles had "hubcaps", which were caps to cover your hubs. Even 2wd cars had those.

I think the "bearing/hub" unit assembly or whatever it is refers to the fact that the bearings are non-servicable. You don't clean and repack the bearings, right? Supposedly they are permanently lubed, and when they wear out, you replace the whole bearing/hub unit assembly.

 

Hmm guess I've been put in my place then.

 

As for backing up to get out of 4x4, never ha to do it with my 98 or 01. Could it be you have a vauum leak on the unlock line or a bad solenoid for the unlock?

 

Some are more touchy than others. They will eventually unlock going forward. Might be 10 feet or 1000yards. A few feet in reverse WILL unlock them however.

It's aight man, heck I thought the same thing as you for awhile till I had to do ball joints a few years ago.

Adrianspeeder

 

Thanks for the replies! I just bought the truck and was trying it out in a parking lot, so I didn't try driving it forward very far. Though reverse it would unlock right away. I checked the vacuum lines with a vacuum pump and they hold vacuum. Will try checking the lever on the diff. and see if it moves ok. The truck has 160k miles so maybe its sticking in the diff? I will check tomorrow.

 

That might be a clue right there. If it was a paved parking lot, or other surface with good traction, you might have simply put your drivetrain in a bind, especially if you tried to turn while in 4wd. By backing up a short distance, you would help to release the bind.

Probably once you shifted back to 2wd, it would eventually complete the shift even without backing up. Routine driving with stops, starts, and turns would probably work out the bind or tension eventually.

I for one am glad Ford has begun using a type of locking/unlocking hub again, as of '04. Among other things, it should dramatically increase the life of the CV joints to nearly forever. Especially for those who lift their trucks, which normally increases the stress on the CV's due to the increased operating angle. With some sort of unlocking device at the hub, the CV's won't be turning the vast majority of the time, unlike with CAD systems.

 

I'm also glad Ford still uses a Dana 60 under the front end of the superdutys...