i have found that when i go from 4x4 too 4x2 my front hubs will take some time to unlock on their own. so what i do is simply back up about 20' they will unlock and then i can go forward in 2wd.

 

Correct, the rear wheels don't need to spin for the front to engage. But the front wheels do not need to turn for it to happen. The front axle needs to turn a little (maybe 1/8 of a revolution?) but it doesn't matter if the wheels are turning or not, the hubs will lock when the axle turns.

And I'm pretty sure thee OP was correct about the potential delay in shifting out of 4WD. I know for a fact that the electronic shift t.case in my '95 F-150 would stay in 4WD for a long time at times before it would actually disengage. Unlocking the hubs was necessary at times. Now my lever-shift '97 F-250HD is similar, although it never seems to stay in 4WD for miles like the F-150 did. I haven't had the t.case apart, but it acts like moving the lever just spring-loads it to shift, but it won't actually shift until the friction in the 'case is less than the spring force. On the plus side, it shifts much easier than the Model 20 t.cases my '75 CJ5 and '71 Bronco had, or than the Atlas that my Bronco now has. All of those t.cases are actually in 2WD when the lever moves, but most of the time you can't get the lever to move until the drivetrain unloads. With my '97 the t.case lever always moves easily from 4WD to 2WD. More evidence I think that the lever isn't actually moving the gears directly.

 

The (automatic) hubs won't unlock at all until you back up (and on my '95 it only took a foot or two). But you don't need to unlock them every time you shift into 2WD, it's fine to drive in 2WD with the hubs locked. But as I noted above, sometimes unlocking the hubs does help unload the driveline to the transfer case will actually go into 2WD.

 

 

Thanks for the replies guys (and gals?). I may have a different style of front hubs because it is very clear to me that when I get stuck in 2wd, engage the 4wd lever, then hit the gas pedal the back wheels will spin part of a rotation before there is a thunk noise from up front and as soon as I hear the thunk noise the truck starts moving forward.

When I throw the lever to disengage 4wd the lever moves as soon as I push it regardless if the drive train is bound up or not. When I had a S10 Blazer you could not move the lever until the transmission was unbound, and it usually took several tries to get it back to 2wd, and it would not go back to 2wd until you had been driving in a straight line for a while. This tells me that even though the lever (and light on the dash) shows 2wd it may not actually be in 2wd yet.

Thanks again,
Blane

 

That's from the front driveshaft needing to turn a little to engage the hubs. The rear driveshaft is direct-coupled to the front, so the rear tires will spin during that time as well. But the way the hubs work, it's relative motion between the front axle shaft and spindle (I think, possibly the hub though) that's needed for the hub to engage.

This points to one of the main weaknesses of auto hubs. That "thunk" noise as the hubs lock is beating on the hubs pretty hard. If you do that often enough you will break them. It's a lot easier on them to put it in 4WD before you get to the point of being stuck. Or if you do, ease into the gas really easy after putting it in 4WD to try to lock the hubs without the "thunk".

By the way, every time you change direction the hubs unlock. If you are 2WD they unlock and stay unlocked, but if you are in 4WD they still unlock, but then they re-lock again right away. So "rocking" with auto hubs repeatedly bangs on them as the unlock, you spin the back tires, and bang the front hubs back in again.

Tells me the same thing.

 

Having torn down the electric Borg-Warner 13-56 transfer case that came in my 96 F-150, and having rebuilt a manual shift model to take the place of it, I don't recall there being anything spring-loaded in the geartrain. Everything is directly actuated by the shift forks which are moved either by a lever on the manual models or by a jackscrew on the electric models. There's nothing spring-loaded about it except for the detent rod on the manual cases that provides for the positive "feel" of engaging each position (but has nothing to do with the actual engagement).

Here, have a look inside and see for yourself: http://www.fullsizebronco.com/forum/...se-bw1356.html

Now... important to note: with the ELECTRIC transfer case, when you go from 2H to 4H it does NOT immediately shift into 4H if you are moving. Instead, a mag clutch* engages and spins the front driveline up so that it's rotational speed matches that of the rear (this also causes the auto hubs to engage), THEN the controller will perform the actual shift. This is to prevent slamming the transfer case into 4x4 mode. With a manual case, it's up to you to do that. If you have a manual case with manual hubs and they are locked then the front driveline is already at speed and the lever will go smoothly from 2H to 4H. If you have a manual case with auto hubs (which is not a factory option), it will still go into 4x4 but you'll hear a bang as the hubs slam into engagement (or explode into convenient paperweight-size chunks).

With either the electric or manual cases, you cannot shift between 4H and 4L without stopping, because like I said everything is directly connected. The electric transfer case's controller is programmed to just ignore the request to go to 4L if you're moving, except on older models where the 4L light will flash to indicate the controller is waiting for you to stop. And if you try to shift between 4H and 4L while moving with a manual transfer case, you'll hear an angry grinding sound coming from the (rather expensive) planetary reduction gearset inside the transfer case.

*Magnetic clutch. Just like the one you see hanging off the front of your A/C compressor. There is also an associated speed sensor used with this setup, and all of these components are internal to the transfer case.

I hope I cleared some of that up.

 

Both our '95s have 1356 manual transfer cases, and originally came with auto hubs. Neither of them slammed or went to pieces when we engaged 4HI.

 

Very good advice.

Blane

 

Very interesting. I just don't see how I can immediately shift out of 4wd on a very tight turn with the drivelines bound up, which would be the case since my lever moves back to 2wd very easily whenever it is thrown.

Blane

 

I'm with Blanes. Like I said above, I've never had one of the newer t.cases apart. But I know the electric shift case in my '95 would stay in 4WD for miles at times after hitting the button and having the "4WD" light on the dash go out. It would crow-hop in corners, spin all 4 tires (when I had both lockers in it, probably only 3 but definitely front and rear after I took the front locker out). So yes, I'm sure it was in 4WD.

The lever-shift 'case in my '97 hasn't been as obvious, but it's seemed to stay in 4WD for at least a little while at times. I'll have to play with it some more and see if I can clearly catch it delaying the shift.

 

I don't know the BW 1356 (though the lack of detents in the '87 I'm trying to revive suggests I'll soon learn--thanks Dixie for the link!) but I know the 2/4 coupling sleeve in my Nissan's transfer case is sprung. When you pull the shifter into 4x, you're moving the sleeve directly. Push the lever back to 2x and the shifter doesn't push the sleeve back, it just gets out of its way. If it's not bound up, the spring returns the sleeve. If the driveline is torque bound (or I'm still on the gas) it'll stay engaged until the binding resolves. I assume this is to prevent the driver from forcing the sleeve to disengage when it's heavily loaded and thus damaging the teeth. Again, I haven't studied the BW box yet, but I would not be surprised if they used a similar design.

Oh, and the sticking-in-4x issue? My first Nissan did that too. After it did it for several miles one night (on a dirt road, luckily) I changed the transfer case fluid. It never acted up again.

Edit: Skimmed the BW writeup and saw this spring on the shift fork for what I assume is the 2x/4x sleeve.

 

I know guys who have got in a predicament with the auto hubs. In a position where the truck won't move and the hubs won't engage..
And I see a couple of you mention disengaging the hub to let the torque off the drivetrain. Do you want to elaborate how you can turn a hub out if there is enough torque the T-case won't disengage?