As others have said, this is a very weird TSB to exist, it refers *only* to 4A systems, but it makes not sense as there isn't anything different to a regular SOF case so far as the IWE's are concerned.

 

I can see one scenario where an argument could be made for this seemingly stupid TSB. With a conventional T-case, assuming you select 4H on the go, the case engages first (getting the front assy turning) and then the IWE's engage immediately thereafter. In the case of selecting 4A on the go, but in a no slippage environment, the IWE's engage against a stopped half-shaft(s). The result is similar to what happens with a vacuum loss, they grind going in. I personally don't use my 4A position. It's either in 4X or out.

 

John, thanks for posting the TSB - I initially saw you posted this in one of the other IWE threads. Just recently I started having issues with my IWEs again. I get the rubbing sound / wet brake feel that goes away as soon as engaging 4A/4H. I went back to one of your old threads to see where the solenoid plug was and pulled it. I circled below what I disconnected - Can you confirm that was correct?

The reason I ask - It definitely did fix the issue, however, the one thing I observed is that steering felt noticeably heavier. I kept it disconnected for a few weeks until I saw this TSB the other day. I plugged that connector back in and pulled the hose and capped the ends per the TSB. It could totally be in my head but my steering seemed back to normal and lighter afterwards. I now really cannot tell any difference from when the IWEs were disengaged (have not compared mpg yet). I'm wondering if I pulled the wrong thing before or is this steering thing just in my head?

Either way, I'm happy for now and plan to roll with this going forward. I don't see any upside to replacing IWEs every 30 to 40k miles or sooner. Obviously agree with everyone that is ridiculous that Ford let this POS system live on for as long as they did and are punting on the fix.

 

I am pretty sure you are wrong in the assumption on how the 4A works in Ford trucks. According to all of the information that I am reading, when 4A is engage the IWE are commanded to locked the hubs the same way if it was in 4H. The transfer case has an AWD function, using clutches is allows the truck to disable output power to one or both front wheels. This intern allows the wheels to spin at different speeds so you don't bind the front axles while turning. According to the manual and other information that I can find on the 4A transfer case, in theory you can just leave it in 4A and it will just effect your gas mileage. Using 4H or 4L on pavement risks possible damage to the front axles/transfercase as it was not designed to work with out wheel slippage. Please see below description of 4A (AWD mode on the F-150):4A (4X4 AUTO) – Provides electronic controlled four-wheel drive with power delivered to the front and rear wheels, as required, for increased traction. 4A tuning varies based on selected Drive Mode. 4A in Normal and Sport is appropriate for all on-road driving conditions, including, dry road surfaces. 4A in Snow/Wet is appropriate for slippery on-road conditions such as snow and ice covered roads.

4-wheel-drive Auto with high range gearing (1.00:1) Full-time all-wheel-drive capability,

Electronically adjusted torque split to front & rear wheels, Electronically variable center differential,

Front driveshaft & rear primary driveshaft allowed rotational speed difference,

4-wheel electronic traction control system is enabled

In 4A mode the center differential is electronically-controlled and rear drive wheel bias. The on-board computer monitors for any sign of rear drive wheel slip (loss of traction)

 

Well, I did have to pay for a battery. Did have to pay for the installation just the battery! So, I guess winner winner chicken dinner again!

 

I think I understand the system fairly well. When commanding 4H, the front shaft spins up before the IWE's go in. In 4A the IWE's are always in but the front shaft powers in and out based on commands from Traction Control. The engagement command comes when it detects rear wheel slippage. The catch comes when you select 4A as a preemptive measure, before rear wheel slip occurs. The IWE's are attempting to engage against a stopped half shaft and will grind in the process of getting the shafts spinning. In 4H the shafts are already spinning when the IWE's go in. As an experiment I'm kind of tempted to hook the IWE's directly to vacuum (just circumnavigate the control sol.) so they can't engage and then select 4A and see if the front shaft starts rotating immediately or not. I suspect not. Maybe I'm completely full of it but after going over the sequence of operations this is the only difference I can think of between the 2 different T-cases with regard to the timing of IWE engagement. I will say with certainty that the T-case has zero control over right/left power distribution to either axle. That's a function of the differentials, biased by traction control.

 

If your statement was true, then when I was having the problem with my IWE grinding engaging 4A would not corrected the problem. But it did, if I left the truck in 4A I had no issues with the IWE grind, but with in a minute of disengaging 4A to 2H the grinding started (due to a bad check value). When I was talking to the tech that worked on my truck 2 days ago. It was explained to me that then you engage 4A the IWE are command to lock (IE resolution of the grinding sound) and operation of the front tire spin was controlled by the TCU and a clutch system to allow the truck to biases the rear wheels intern allow the front wheels to spin a different rates. The person that I was talking to could have been BSing me, but it made senses and when using 4A in my truck I don't think I have heard any grinding from the IWE.

 

All this is true, except for the part about the front shaft not spinning, thus rendering the rest untrue. As the Tcase front/rear connector is electronically controlled on a clutch instead of mechanically locked in the regular SOF tcase, when you select 4A, the axles engage perfectly, as the front half shaft is already spinning, just not torqued up.

To clarify, the front half shaft and axles spin nearly all the time, even in 2H.

 

I'm having a hard time with that. I have two ESOF trucks, one is TOD. Even on the TOD truck nothing turns in 2H. On the couple of occasions where I have caught something turning in 2H, its been due to a loss of vacuum to the IWE's. Usually a failed control sol.
-- After watching the video linked below, yes maybe the TOD might experience some coasting of the front shaft due to fluid drag, however mine does not. At least not on the occasions I've checked it warm. Maybe it would if cold enough, I've never checked it cold. Even if it's coasting to a degree, the IWE's are still having to pull the shaft up to speed and that's where I think the grinding and wear is happening, and the underlying cause of this scab of a TSB.

 

Typical IWE grind occurs as a result of a partial loss of vacuum to the front end. There's not enough vacuum to hold them out, but too much to let them them fully engage. As a result the couplers are dragging the face of the drive collar and it sounds like a spinning ratchet wrench. It's a fairly common problem and I've dealt with it on multiple trucks/occasions. Selecting ANY 4wd mode cuts vacuum completely and they drop in and become quiet, regardless of which T-case you have. The issue being addressed in the TSB, as I understand it, is an entirely different issue and related to the sequencing of engagement between the IWE's and the T-case, which is different between the conventional case and the TOD case when selecting 4A. When selecting 4A on the go, in no-slippage conditions, I believe the issue is the IWE's engage BEFORE the front shaft spins up and they're getting chewed up over time. It's not the ongoing chatter (like with a vacuum failure) that's being addressed here. It only happens briefly as hub engagement occurs but the cumulative damage is showing up now in some trucks after years of use and numerous cycles.
PS - With regard to your first sentence, I don't know you connected those dots. I've repeatedly said that selecting any 4wd mode will kill the IWE grind (assuming it's a vacuum problem) by engaging them. I have always espoused that and never said anything to the contrary.