Update
They just got to it even tho they've had it since Tuesday. They were unable to recreate the problem so I had to go in and do it for them. But the tech riding with me was immediately pretty sure he knew what the problem was once I recreated it...good news: not the transmission.
It sounds to him like there's a failure in the 4wd vacuum system. Apparently the hubs default to 4wd as that's seen as more useful (if the system fails they want it to default to 4wd in case you're stuck somewhere). So in 2wd the vehicles run a vacuum to hold 2wd. It sounds to him like the system is leaking somewhere so it's losing the vacuum and the hub on the front driver's side wheel is trying to engage. That's the scraping/grinding noise I'm hearing, the hub attempting to engage while moving. The system isn't showing 4wd because the transfer case is still in 2wd, it's just that individual hub trying to engage because the vacuum that holds it in 2wd is failing/failed.
So, they have to tear into the 4wd system and see where the vacuum is bleeding off, fix that, and I should be ship-shape.
Annoying, but reassuring it's not something more serious like the transmission.
I know there are some seriously mechanically-minded folks on here...if that scenario sounds reasonable, please let me know. If that sounds like hogwash, that would also be helpful to know.
I’m skeptical. I’ve worked on the vacuum hub system, my 2007 has the same setup. Most fords from the early 2000s till now use this setup so we know them pretty well at this point. It is true when a hub is half engaged half not it will grind. Normally it is at random and upon turning etc. But what concerns me is you say it is specifically in 2 and 3 gears and now shifting to reverse. They will not grind unless they are spinning as well does it grind in reverse right away upon shifting?
There is a 4WD solenoid that vents vacuum to atmosphere on our trucks when they are shut off. (When off the hubs lock due to lack of vacuum). Upon startup the hubs disengage when vacuum is present, in 4A however the Solonoid will vent vacuum and hubs will engage so that the front axle is on standby when power is sent forward.
It’s plausible yet this isn’t how the system normally fails as you describe your issue. The system will grind if an actuator is not engaging the with the hub completely, this is often caused by a seal failure in the hub actuator. My main questions are these:
Is it specifically at the gearshift s you mention?
Are you rolling in reverse when you experience the grinding or is it upon shifting?
If your answers are that it’s when rolling and Not specifically at gearshifts then it is very possible. Please view the attached:
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