4405 Transfer case Auto not engaging

[joecrna]

Noticed this starting a month ago turning right on a wet road. Rear tires spun easily, fronts didn't seem to pull at all. Took it to the dirt and sure enough, front axle never engages in Auto. In 4WDhi or 4WDlow it works as it should. Front axle locked to rear.

This seems to point to the GEM, solid state clutch relay or one or both Hall effect sensors in the transfer case.

A few months ago the transfer case stuck in 4Lo while out of town on business. I had to drive it this way 40-50 miles (slowly) to the nearest Ford dealer. On my way back home I stopped and picked it up. They replaced the transfer case shift motor (motor assembly #YL2Z,7G360,A) and sensor- man. lever (#F7LZ,7F293,AB). I was told it was the transmission position sensor and something about a Tone Ring, total $915. No tech was there at the time, but the service writer seemed fairly knowledgable. I assumed this was in regard to the transmission range sensor at the time.

Now I wonder if this could have been the tone ring for the Hall Effect sensor in the transfer case. Any help trouble shooting this would be greatly appreciated. In any case, this seems like another expensive dealer fix. Or potentially expensive if I just guess at Hall effect sensors, GEM or clutch relay. It is unfortunatly a daily driver, so I can't just tear it apart and play with it for days.

Sorry for such a long question but I was hoping to provide all info that may aid in a response.

 

[Glacier991]

Joe.... the dealership practically sounds like they were throwing parts at this problem. That may he harsh, but you can test a DTR sensor with the Rotunda transmission tester, for example.... to just replace it was silly unless it tested bad. Similarly the shift motor has noting to do with Auto operation. I am betting the old was was just fine.

I had to go back to the 4405 Rebuild Diary above in the stickies and re-read the FORD explanation of the inputs into the auto operation. It says:

Feature inputs:

* 4WD mode switch.

* Transmission range (TR) or digital transmission range (DTR) sensor.

* Vehicle speed sensor (VSS) switch.

* Front/rear driveshaft speed sensors.

* Contact plate position inputs A, B, C, D.

So from there, I would have tested the switch, and the DTR range sensor. A bad VSS *should* throw a code (but never say "always") but I doubt that is it. Then you have the contact plate positions (which I think is referring to the shift motor) which I am guessing act to inhibit auto operation in a 4WD locked mode... and finally the GEM and Hall effect sensors. Hall effect sensors are pretty reliable, but again never say "always". A tone ring is nothing more than a notched tooth gear - I cannot imagine how one can go bad unless it was damaged somehow.

I think your thinking is on the right track. I'm sorry you invested what was probably an unnecessary $915. All that said, what you will be doing is trying to eliminate everything but an internal mechanical failure in hope to avoid a teardown.

I fear there exists a very distinct and good possibility the ball ramp electromagnetic system is busted... or the electromagnet has a problem (less likely). The ball ramp setup (see the 4405 Diary for pictures) is a known break point.

 

[joecrna]

Glacier, I guess my description of the problem was bad;

The dealer replaced parts were for a seperate problem. The TC was stuck in 4Lo. They did supposedly test the sensor (bad). The shift motor I would assume was bad, wouldn't shift out of Low range. All this fixed the problem I had then (stuck in 4Lo) but shortly after they fixed that problem, I noticed the new problem (No auto function).

The Transfer Case works properly when placed in 4Hi or 4Lo. It just fails to engage the front axle when in the Auto position. This seems to rule out a bad ball ramp or electromagnet. I have no codes, so the VSS seems to be ruled out.

I was wondering if the parts they replaced could have led to an improperly installed tone ring. They may have missed a bad Hall effect sensor. However, until the TC got stuck in Low range, all was working well. Perhaps alot of heat driving it to the dealer. How would I check hall effect sensor function or the tone ring. Probably requires a teardown.

This only seems to leave the GEM. How would I check its function, short of just installing a new part.

 

[Glacier991]

4Hi or 4Lo use the fork to actually move a shift collar and engage real gears. The ramp is used in auto mode, so it could be the ramp even if you have 4 hi or 4 lo. I am not saying it is. But it "could be". With the new info... I am stumped.

You "can" test hall sensors, but I'd have to dig out the test process... not too tough as I recall. As for testing a GEM, That would be new teritory for me... but I'd guess it is replace and see.... a damn poor way to fix autos. Maybe someone more knowledgeable on GEM's can help us here.

Sorry I am not more help.

 

[joecrna]

Thanks for your response. I didn't realize 4 hi and 4 lo don't use the ball ramp. I thought they just sent a 100% duty cycle to the electromagnet. Now I really don't understand how the brown wire mod works. I thought it just eliminted the power to the electromagnet. I'll have to take a look at the 4405 rebuild diary again. When my girlfriend replaces the Explorer as her daily driver, maybe I'll have to tear the T Case apart and have a look for my self just to understand better.

 

[Glacier991]

Mind you I do not claim to be a TC guru. But having rebuilt one I think I am correct about the operation of the TC. Go read the FORD description at the top of the Diary and look at the pics. When the fork moves the collar up or down and engages the respective gears lockup is positive as I best recall, not clutched. I thought the clutch was for Auto only... and hence the electromagnet only operated as an "on demand" situation.

The Brown wire mod was designed to eliminate that now and then lockup/partial lockup (with no user control) as I understood it.

But now you have me questioning my own understanding. IZWACK or Glfrederick or GIJoecam can probably straighten me up here. Don't take my word on TC's as gospel.

 

[Glacier991]

Well I just went and read the brown wire Mod.... and it certainly appears you are correct. The shift collar only manages HI / low, and the clutch does the 4WD/ 2WD thing. Mea culpa.

Knowing that, not having 4WD in auto does NOT implicate the ramp assembly, but probably the switch or GEM, in my opinion. (And now you see what MY opinion is worth.)

 

[joecrna]

Your opinion is worth quite a bit. Your write-ups even more. Incredible detail, the pictures are incredible. The confusion stems from how the 1354 TC functions. Here the shift motor moves the fork to both select 4 WD and Hi/Lo range in the TC.

In the 4405, the auto mode is either zero (very little) or 100% duty cycle for the electromagnet. To provide front axle lock-up when in 4Hi or 4Lo the GEM simply sends a 100% duty cycle to the electromagnet and energizes the ball ramp clutch.

I think I'll pull the shift motor out and see if maybe they crushed a wire to that one hall effect sensor that I saw under the motor in your pictures. It just seems the Auto system doesn't know when the rear tires are spinning relative to the front.

Thanks again for the discusion. I may not have an answer yet but at least I am becoming more focused on possible culprits. I certainly have a better understanding of how the TC works.

 

[gijoecam]

Sorry for getting in here late...

Glad to see Glacier figured out he was wrong about the lockup... If it locks in 4high and low, we can eliminate the clutch coil or that part of the assembly as a problem.

I would concur that we have an electrical gremlin to ferrett-out here.

I do not, however, think it's a sensor going bad. In my experience, when a sensor fails in either the t-case or the rear axle, the system first defaults to a locked setting (because it thinks one axle is spinning while the other isn't) and after a short time of not being able to detect both axles spinning the same speed, it throws a code and disables the system as indicated by the blinking lights. (had that happen to me last fall) Being that you're not getting blinking lights, it leads me to believe it's an issue with the GEM or TOD relay. So, let's start there.

Check a few fuses... Instrument panel fuse panel, # 28 (7.5A mini), #10 (7.5A mini), and #20 (7.5A mini), power distribution box fuse # 4 (30A maxi) (I doubt that's bad, but you never know). The next place I would check would be the torque on demand relay... If you yank the stereo out, remove the trim around it, and remove the upper vent plenum from the center of the dash, you'll see the TOD relay in the upper right hand corner of the opening. Check for any obvious signs of wiring trouble... If you can get the relay out of a donor vehicle, I'd swap it out just for peace of mind. There is no easy way to test it outside the vehicle because it's a solid state unit.

Now, it's tough to test much beyond that... For more info, one would need an NGS or WDS scanner to be able to view the GEM PIDs (inputs and outputs) to see what exactly the GEM is (or isn't) seeing and how it's responding. That takes a sharp tech with the right scanner and some time and dedication to troubleshooting it properly (not an easy thing to find). But start with the fuses and let us know if you find anything...

-Joe

 

[joecrna]

I'll start with the fuses Sat. Like an idiot, I never bothered to check those. Im out of town right now but I'll get on it first thing Sat. May have access to needed scanners Mon. I'll keep everyone updated. Don't happen to know what a new GEM costs do you. At $100 an hour for the tech, just replacing it if we can't find anything else wrong may still prove cost effective. I hate to do it that way though.

Once again, discussing things with people on this forum proves immencily helpful.

 

[joecrna]

My path crossed my girl friends while on the road, so I checked the fuses. All OK, figures. I'll check on the NGS scanner this weekend. Got to love learning how to use an expensive scanner you'll never be able to afford and probably never need again. Keep you all updated.

 

[joecrna]

Joe

Does the TOD relay energize the electro magnet when switched to 4Hi? If so wouldn't this seem to indicate the TOD relay is functioning?

This leaves just the GEM, or a sensor. Unless there is some pathway from the GEM to the electro magnet that is not common between auto and 4Hi.

If I can't get access to the NGS scanner this weekend, I am tempted to just swap out the GEM. Probably cheaper than paying the dealer to run the diagnostic.

 

[gijoecam]

Based on my understanding of the system, and the experience of a few others on this board, the Transfer Case Clutch Coil is powered by BOTH the TOD relay and the GEM directly. The power wire for the TCCC is spliced together with both the feeds from the GEM and TOD relay. If you skim down the pics in the Brown Wire Mod thread, you'll see where I point out this splice in the photos.

When the BWM discussion first came up on here a few years back, someone had clipped the brown wire right where it comes out of the TOD relay. What they found was that when they cut the feed from the TOD relay, they still had 4high and 4low with the switch off. Effectively they eliminated 4auto, but not 4high/4low because the power for the TCCC came right from the GEM (or at least that's what we surmised happens).

Swapping out the GEM is relatively simple. If you look at the pics in the BWM thread, you'll see the GEM and how it's installed... It shouldn't take more than about 20 minutes to swap one out, but they're not cheap... Heck, the diagnostic might be cheaper. I hate throwing good money at a problem without knowing for sure the part is bad...

-Joe

 

[Glacier991]

Its a shame that increasingly the proprietary nature of testing (not saying necessarily that the NGS is such, but one is pricey and the only way to test a lot of things) versus the cost of a test relegates one to replace and hope. Like Gijoecam, it makes my skin crawl to diagnose and fix things that way. But...

 

[joecrna]

No access to correct scanner for this. GEM is $319 locally. Alittle more noodling this over, a few basic circuit tests just to make sure its not something simple, then its decision time. Maybe a couple hours of diagnostics at the dealer is all thats left?

 

[joecrna]

Took the Explorer to the dealer. Agreed GEM, TOD (called Transfer case switch relay in Ford Computer, $58) were likely problem. The tech seemed very knowledgable. He said he hed seen several failed Hall sensors in the 4405 and thought the ABS sensor in the rear differential was also a possibility. I had already checked ABS function and discounted this. Used NGS scanner and found open circuit for ABS in GEM. Solution is to replace GEM, they have one in stock. Total cost for diagnostics, GEM and labor is just under $600. I'll let you know if this fixed the problem when I get the car back. Thanks for all of you're help. At least I seemed like I knew the 4405 TC inside and out when I went to the dealer.

 

[joecrna]

During final inspection before giving me back the Explorer the dealer found eratic readings from the Hall effect sensor for the front output shaft. Another $150 and two new hall effect sensors. Seems all is functioning well now.