Electronic 4x4 problem/Question

Wwblue05

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Hi, I am a newbie here, registered several months ago looking for help with typical 6.0 engine problems. My truck is an '05 SB CC automatic with electronic 4x4.

My problem, and Q., is about both the electronic 4x4 controller and the locking hubs, especially about how the hubs, electronic controller and transfer case all work together. I am pretty much in the dark about how these work, particularly what the hubs are doing when you manually lock or unlock them. When we went to get this truck in July '05, after buying it new over the internet and phone, the 4x4 module was bad and the dealership replaced it. There were only about 100 miles on the clock then, most of that with the salesman driving the truck to meet us. I suspect the 4x4 module is part of the problem now, that it just bit the dust, again. I do not go off-roading, but briefly use the shift-on-the-fly farily often on a dirt road short cut from highway to the road i live on. The dirt road goes uphill toward my house, and is very rocky, so I use the 4x4 so as not to chunk one of the rear tires, and to exercise the system. I live on top of a ridge and also occasionally use the 4x4 to get up the hill of my back 1 acre, especially with a trailer. Last summer, when parked in my yard at a slight incline facing downhill, in dry soil/grass, the limited slip did not lock up when I tried to back up, digging a rut with the right rear. Then the 4x4 would not engage until I tried it several times ( trying to get it into 4wd H or 4wd L, either one, putting trans in neutral with foot on the brake. The manual does say or imply the 4x4H will not engage with the truck stopped - which seems pretty useless in some cases, but this procedure is how a service manager told me to get it engaged at a stop).

Today I parked near the same location as the above, but at a steeper incline and on water-logged soil and grass, with back of truck facing down hill. I knew I would probably need the 4x4 to get out of the situation I parked in today, it is extremely wet, but the 4x4 seems to have been working well since the occasion last summer. When I turned the knob to 4H, then to 4L, there was no typical clunking of gears engaging. Four or five attempts at shifting into 4x4 all resulted in just rear wheel spin, digging holes (about twice as deep on right as on left). I checked the fuse #31, for the 4x4 and it looked good. I put in another fuse just in case, and same result - no shifting into 4x4. In desparation, I locked the front hubs, which I have rarely done, and really don't know when or what situation would normally dictate locking the hubs. Normally, I have not needed to, as everything seems to have worked well just using the electric shift knob.
After locking the hubs and shifting to 4H, the front wheels pulled and I got out of the mess I was in. However, I still heard no reassuring clunking of the 4x4 mechanism, and it would not go into 4L at all.

I read everything in the manual about the 4x4 system, though it has almost zero information about the locking hubs, what is actually happening in using them, when or why they need to be locked. I have searched on a couple other forums as well as Googled the subject, with no answer to my specific questions and situation.

Q's: Does this sound like the 4x4 control module has quit? 2. How is it that locking the hubs made a difference when the electronic controler does not seem to be doing anything?

The truck has a little under 82,000 miles, and is on an Extra Care warranty which I believe covers the 4x4 module, but I am just wondering why locking the hubs made the 4H work, and if it is very common to have problems with the module.

Thanks for any info and help. I will post pics of my truck when I can figure out how to get that done, tried before and couldn't get it to work.

Joe
 

KRISTOLSON

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Sounds like an auto hub issue to me. That would explain why it seemed nothing was happening at all until you locked the front hubs in manually. You just experienced about the only situation I can think of that would dictate manually locking your hubs- when the auto lock doesn't work!

A quick run down of the system, starting with the t-case-
The t-case shift is carried out by an electric actuator. These are pretty reliable units, but have been known to go bad from time to time. It is very possible for it to shift into 4x4 without making much noise, especially if you are not moving and the front hubs are not engaging. When you turn the switch, if the 4x4 indicator lights on the dash light up, that would indicate that the actuator has moved to the correct position, and the shift is happening successfully. My truck has always been very fussy going in and out of 4x4 low, seems like it always takes some back and forth rocking to get it to go in or out.

Now the hubs-
When you turn the switch on the dash to 4x4, the hubs are supposed to autolock. When the switch is turned off, the hubs should unlock so the front driveline is not turning. Ford uses a vacuum diaphragm inside the hub to actuate the locking and unlocking of the hubs. It is basically performing the same task as turning the switch on the hubs manually, but with a vacuum pulse.

The best way I can describe the mechanism inside the hub would be like clicking a pen. Your thumb is the vacuum diaphragm, pushing in on the hub. One vacuum pulse will pull in on the hub and it "clicks" in and holds when the vacuum is released, just like the point of the pen stays out. When the truck wants to unlock the hub it provides a second pulse of vacuum, "clicking" the mechanism a second time and just like the pen it retracts when the vacuum is released.

Lots of things can go wrong with this system, but the most common problem that would cause the hubs to not engage is a vacuum leak, either from a broken vacuum line or bad hub seal. I have also heard of the vacuum valve that controls the vacuum pulse to the hubs going bad, and the diaphragms inside the hubs on my truck have failed in the past. Sounds like the dealer will take care of this for you, but if you want to check it out yourself, the first place I would look would be at the vacuum lines. The line runs from a vacuum ballast tank and 4x4 valve on the passenger side of the engine, down to the frame under the engine, where it tees off and one hose goes into the back of each hub. On my truck one anchor came loose and my line melted on the passenger side exhaust manifold.

An easy way to check for vacuum leaks in the 4x4 system is with the truck running, put your heat/ a/c to the vent setting, then turn the 4x4 switch on. Since the heat/ a/c is run on vacuum, if there is a leak in the 4x4 system it won't have enough vacuum to hold the door in the vent position, and the output of air will change to defrost for a bit, then back to vent.
 
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f100cleveland

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Sounds like my truck. It stays in manual lock all winter and I just turn 4x4 switch when I need the front to work. The 4x4 lo range has been nearly imposible to get to engage since new. I believe my module is bad too. Ford posi's are junk


Krist does know his stuff.
 

Boadie

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IIRC... Another reason to use the locks is 4 will not engage without a complete revolution of the front wheels without them.
 
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KRISTOLSON

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Like F100 said, the ford limited slip is not very "active". If just one of the front hubs won't engage, your 4x4 will be almost nonexistent.
 

Wwblue05

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Thanks for the info and insight from all of you guys. Since my first post on Sat. 3/30, I tried the system again on Sunday, on a steep wet grassy shoulder of the ridge road I live on. It seemed to work alright, without manually locking the hubs. By that I mean that I could tell by the way it drove out of the spot it was in, that 4L had engaged, then the same in 4H. I still did not hear any clunking shifting in or out of 4x4. I think at times I have not heard the shifting noises, but most often I have, I would guess 60-75% of the time I would hear the noises. The strange thing is that I have not had to lock the hubs to get 4x4 operation, with the possible exception of last summer in the situation I described in the OP, tho' I don't remember for sure if I locked them or not, just had an afterthought that I did have to lock them.

After that episode last summer, in which I took photos of the ruts the rear wheels dug in my yard because the Ltd. slip wouldn't work, and at first the 4x4 wouldn't engage, the Service Mgr, and the tech at the dealership, never told me anything definite about why it wouldn't engage and just spun the right wheel. So I did some reading on whatever forums I could find info, maybe it was some on here, about Ford's Ltd. Slip. I think it is true that Ford's system is not really very good compared to GM's. I watched a Youtube video with some guys comparing Chev-Ford-Dodge limited slip/positract out in a river bed area. They were going across a little rivelet, like a bar ditch, in the sand, that was maybe a couple feet deep and a few feet across. They were crossing it at a diagonal, which would put the right rear in the air for a short distance, and make it very clear which wheels were pulling and which were not. The Chevy was the only one of the three that crossed without drama and wheel spin. It just quietly and easily crossed the ditch, no wheel spin at all. Since I have another ESP warranty, purchased last summer with 76,100 miles on the clock after we had to pay for the oil cooler/egr cooler and valve, and fan clutch debacle, I hope that if my 4x4 acts up any more that they will do something about it. As with the ABS light that often comes on after a couple hours driving out of town, then goes off before I can get it to the dealer, supposedly because of the sensor in the differential, they tend not to fix anything they can't see malfunctioning at the dealership.

If I have any further trouble with the system I will post about it. With all I have to do though, I probably am not going to spend much time trying to diagnose the inconsistent behavior of the Ltd. slip and 4x4 for the time being. I'll just say that there is something about the truck that doesn't like that particular area in my yard at the edge of the hill where I park sometimes to be in the shade or near my little shop building. LOL.
 

DaveBen

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You can get the limited slip to engage, when it spins, by lightly putting pressure on the brake pedal.

Dave :)
 

Wwblue05

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You can get the limited slip to engage, when it spins, by lightly putting pressure on the brake pedal.

Dave :)

Thanks Dave. I had read that before, but forgot about it. Hopefully will remember that next time in a similar situation. Joe
 

DaveBen

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It works if you do it by applying light pressure while the wheels spin. Try it and let us know how it worked for you.

Dave
 

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