Encoder Motor-'04 TB may have gone into 4Lo on expressway....

[mustangrosey]

Ok, brand new here--tracking down Roadie from that other site.

Situation:
We've been having Service 4WD light for a bit, selector lights still lit up, and usually the drivetrain would go into the selection. Did have to do the #8 fuse trick, and had replaced actuator. Most recently, the lights would blink when making a selection, but return to solid at the previous setting. Service 4WD light would not come on for about 50 miles when driving. About 6 days ago, the TB would not come out of 4wd. About 4 days ago, husband removed encoder motor (left hooked up) to manually move back to 2wd. We decided to leave it in 2wd until we could work on it. He put it back in, all lined up. About 2 days ago, I am driving to work on the expressway, and suddenly the rpm's go up to 4grand, and it was like the TB had been accidently shifted to neutral (but hadn't). I though the used tranny we had put in over the summer had gone bad. Pushed accelerator, no response, just high rpms. So I get to the side of the road and wait 3 hours for a tow to deliver the TB and me, to where I work. As I was on the side of the road waiting, it seemed like, when I had put it in park, it seemed like it sort of "slammed" (I was at a complete stop), and I thought I had lost park. So I kept my foot on the brake the entire time (with motor off).

When we got to where I work, the tow driver was unloading the TB, and tested park. He said I hadn't lost it. We backed into the only open spot. and I was able to borrow a company car for the nite. Next day, our maintenance team wondered if I had any gear and would be able to move it to an end space so they could plow the lot. I attempted it, it went forward in drive. Parked it in the end spot and borrowed the car another nite. Today, my husband and I went to check it out (we live an hour from there, and the TB is our only ride right now). He gets in it, backs it out, goes forward and back in the lot, and says it is in 4Lo! Indicator was on 2Hi, but light was on over 4lo and never went out. Did this thing slam into 4lo on the expressway??? (I heard no noises, had no sudden slow down other than loss of "forward" as if in neutral, and heard no "nashing" or clanging I would have expected.) I'm trying to figure out if the safety brake on the encoder motor was bad! He said that the encoder motor moved freely when he had it out. Not sure if the problem is encoder motor or tccm, or both. (We have the indicator lights, yet we had the service 4wd light until after he got it back to 2hi manually.) He's going to have to do these repairs in the parking lot where I work! Don't want to have to rent a trailer, or have it towed 60 miles! If we change both, what symptoms would we have if the TC is trashed?

 

[IllogicTC]

There are a couple things running around in my head from the info provided so far. Don't go running with it, it could change or someone could correct me, or Roadie will hero his way in here and ask a few questions that would make the problem more specific, too. It's strange since there are shift interlocks in place to prevent the driver from doing this sort of thing - the vehicle MUST be in neutral, and the vehicle MUST be traveling less than 2MPH.

My thoughts:
1.) Intermittently-failing TCCM. You said the service 4x4 system light shows up after about 50 miles or so? Without touching anything like flipping the knob to any other position? That would sound to me like the TCCM is getting goofy, once there's time for heat to build up in the cabin and whatnot, or maybe a faulty class 2 data wire. If the TCCM was going rogue, who knows what it may have done, though honestly I don't think I've seen a story of one becoming "sentient" in this respect before. Maybe I haven't read enough 4x4 threads yet.

2.) Failing encoder motor wiring. The brake itself doesn't set until 4HI is selected. This helps the encoder motor maintain the pressure on the clutch pack. In A4WD the brake remains disabled as the motor itself varies positions, and in 2HI is also off I believe. 4LO, I'm not sure if the brake is enabled when it's in position but I would assume so, again to help maintain the clutches at 100% engagement. A short in the encoder motor wiring may have energized it.

Maybe the 4LO indicator was lying, after all you did say the service 4x4 lamp shows up a bit down the road (without engaging anything, right?) which still says faulty TCCM to me, and if one's on the way out the door I would imagine it could report incorrectly. But I'm sure you'd know if you suddenly shifted to 4LO. The way the transfer case shifts isn't like an automatic transmission - that's part of the reason you have to stop first. It moves a high/low range collar rearward to disengage the high-speed teeth (1:1 ratio, normal driving) and then engage the low-speed teeth (2.69:1 reduction ratio). Imagine having a manual transmission in a car and suddenly forcing the shifter from 3rd to 1st without using the clutch. It's not a perfect comparison but some parallels can be drawn here, and the result at highway speeds would probably be shelling out the gears, and of course you'd definitely FEEL it.

Another thing to note with 4LO is your engine has more leverage over the road. A lot more. Notice how if you're in say, second gear going downhill, it doesn't speed up as fast as being in D going downhill? 4LO would further enhance the engine braking effect (by a pretty sizeable amount, too) so as soon as it flipped over assuming the planets aligned and the high/low collar somehow made a perfect shift at highway speeds and nothing snapped from the sheer stresses involved, you'd definitely get a response from the throttle when you touched it (gear reduction, more leverage over the road therefore quicker acceleration generally), and you'd notice it feeling like it can't really coast.

I'm hedging my bets on the transmission somewhere, with a nice crappy TCCM coming along for the ride but not necessarily part of the problem.

 

[mustangrosey]

Yes, light had been coming on without doing anything, just driving along. (happened in A4wd and 4hi, no light in 2hi, and then it got stuck in 4hi). I agree I would have thought if some safety feature failed (it was only 2 days after he had that encoder motor out) and allowed it to go into 4Lo at a speed like that, I would have had a lot more noise and probably some skidding/loss of control. It is definitely in creeper gear now, and won't come out.
When the first tranny failed, it had similar symptoms, except more like slipping in and out of neutral, getting into "limp home", but this was just all neutral (and I did check the gear shifter to make sure nothing had knocked it into neutral). It was such a busy time of day, I didn't even check to see if I had other gears, I just wanted to get out of the way (and there are large snowpiles everywhere so the shoulders are quite narrow right now) and hope no one slid into me!

 

[mustangrosey]

I guess if it is the tranny again (along with some kind of 4wd issues), the "good" thing is that we kept the old tranny to rebuild it (why "sell" a $800 tranny back to a parts store for a $75 core charge???). It's great to have trained mechanics in the family (though working in other professions)!

 

[mustangrosey]

Yes, I've had to do some manual tranny shifts without a clutch...can't imagine the planets would align like that in this situation...or I need to start believing I have a guardian angel! ...miss my 03GT (mustang)

 

[IllogicTC]

I'm still not entirely sure if the 4x4 and the expressway perils are linked in any appreciable manner. The service 4x4 may be expected in A4WD if the encoder motor fails to achieve the desired position, as it is constantly shifting as speed and driving conditions do the same. However in 4HI click in and stay in. There's no feedback to ensure the brake is enabled or disabled, only for encoder motor position. Even then, the encoder motor's position doesn't determine what the indicator lamps show as far as I know. I do not know if improper encoder installation can cause any such phenomena as sudden shifting, especially since 4HI and 4LO are at opposite ends of travel, oddly enough. You'd think 4LO would be in the 4HI position, just advanced a little further to hit a detent or something, but it's actually on the opposite side of the shift lever's travel.

Have you tried shifting the transmission manually to 1st or 2nd gear? 3rd just locks out OD, but 1 and 2 force the transmission into the respective gear. I'm sure you're familiar with how it feels accelerating from a stop in 1st, and in 2nd it feels kind of like transmission slip from a stand-still but it's not. If you can't get the transmission to at least transition between the first two gears, that's where I'd start. Do you happen to know exactly what speed you were driving when this occurred, and which rear axle you have? You can give it to me in number or RPO code form if you know, and if you're curious, check in the glovebox. There's a sticker on the glove box lid listing a bunch of codes, arranged alphanumerically. If there's a code that says GU6, that's a 3.42 axle. GT4 is 3.73, and GT5 is 4.10. While you're in there, if you there's a G80 code you have the locking rear. Not necessarily related to your issue, but it gives you a good feeling to know what your vehicle's got, doesn't it?

And I'll save Roadie a step and say that A4WD, while having some fairly particular uses, is NOT a recommended setting. Because of the way the transfer case operates in this mode, it'll reduce the life of the system. Instead of acting like a Torsen differential or something, it just partially-engages the clutch to the front driveshaft. Imagine holding your clutch halfway down or something on a manual-transmission car, we all know how well that works out for the clutch in the long run .

And what is the service history on the transfer case? Has the fluid been replaced every 50,000 miles, using the specified Auto Trak II every time?

 

[IllogicTC]

I'm sure our resident 4x4 expert can help illuminate on this a bit more. In the meantime, maybe someone else has some ideas on things to consider or look at, but it usually quiets down a bit around here overnight.

 

[mustangrosey]

I will look up the tranny type when I get back to the car on Tuesday. (Working out of town on Monday.) I think I was doing about 65 or 70, as I was changing lanes to the slow lane at the time. We (well, hubby) will likely take the encoder motor back off in the lot at work, and see if he can manually move it out of 4lo. I guess from there we will be better able to see if we have shifting/tranny problems. Seems like we will need to change the tccm regardless (assuming it goes back on the road at some point with or without a different transmission.) We may also replace the encoder motor while it is out again. (I do assume we will get it back on the road, so might as well take care of those items at the same time.)

 

[IllogicTC]

To get it back toward 2HI, the shaft will need to be rotated clockwise. Our sister site, offroadtb.com, provides an excellent article on the transfer case.

Using the picture of the cam lever on there, it's apparent that there's two raised portions that activate the clutches, you'd need to bring the shaft to just before the 4HI raised part engages. See the photos for the various modes where there's a detail view with an arrow pointing to it to understand what I mean. This is assuming the case is indeed in 4LO, and really it's free to try it so hey, why not?

I myself am still leaning toward the transmission being defective in some capacity and jumping down gears. With the 3.42 (GU6 code) axle, the RPMs would go back up to about 4000 at that speed if the transmission went down to 2nd gear for some reason. 4LO, if the transmission was good and remained in 4th gear, would have shot your RPM up to about 4600. Using offroadtb's gear ratio calculator to provide these numbers by the way, so it's at least a good measure more accurate than pulling numbers out of my hind end,

Before digging into the transfer case, try my idea on manually selecting a gear. If 1st doesn't even work or something, transmission may be a culprit. Also, a test holding the throttle steady and testing for slip may help. If you can really run her up without really getting anywhere or it taking forever to come up to speed while the tach stays the same, there's transmission slip, and it may be another issue that's tied with the first possible issue.