The Expedition expedition continues to see setbacks. Yesterday, the second case magnet sent overnight from Ford's Detroit main warehouse to my local dealer was lost in the same system. Here's my thought on that. It's a magnet about 1" square. If it was shipped in a bubble envelope, it is probably sticking to a steel conveyor frame somewhere, right next to the one sent a day earlier! Nonetheless, I decided to heed the words of my elders - "the Lord helps them that helps himself!" It's a magnet, how hard can it be to cobble something together?
Here's the situation: from the factory, the magnet appears to have been missing (I've owned the truck since new, and the transfer case has never been opened.) The magnet holds the oil pickup screen in place in a dovetail in the case. Here's a picture with the oil pickup in place (a new one) without the magnet:
Here's what happens when the missing magnet causes the chain to saw into the pickup screen:
This was my plan: cut a piece of scrap steel to size, mill a socket in it for a round neodymium magnet from Home Depot, and put the magnet in the socket. Here's what I started with:
I marked the piece and proceeded to milling (on an old drill press, since the mill I have access to is 45 miles away):
Next, I cut the piece to size and cleaned it up as best as I could (the milling was horrible because the old drill press has tons of play in the spindle):
Popped the magnet in:
And put it in the case:
And, I can now finally put this case together and start rebuilding the Expedition - woo hoo! Now, you may be asking, "why didn't sab just do this on Monday to salvage the week off to finish this project?" That's a great question - thank you for asking! There was another part that would have been much more difficult to fix that was also delayed. It didn't arrive until yesterday morning, so this simple part was not my only holdup on the transfer case rebuild, so doing this earlier would not have expedited the Expedition expedition.
I have one more issue I'm working through with this transfer case. I haven't figured out how it all works, yet. It has a shift cam for AWD, 4HI, and 4LO, and a front/rear friction clutch that is actuated by a big magnetic coil. The bias in AWD is RWD until the rear wheels spin, and then the clutch engages to apply torque to the front driveshaft. Apparently, the coil is controlled by a module that senses the front and rear output shaft speeds through Hall Effect sensors and 30-tooth tone wheels. When the speeds differ by some threshold, the coil is activated to either engage or disengage the clutch (I can't tell since the only way to observe the coil action is when the cases are assembled, and then you can't see it.)
When assembled per the Ford manual, which is pretty detailed, in the AWD position, the sprockets are misaligned axially, but the clutch is engaged, so the chain turns the front output shaft. I'm afraid I've assembled something incorrectly, and once I put it together, this thing's gonna grenade due to that misalignment. I've put this thing together about a dozen times (remember I had all week to kill waiting on parts), and each time I end up at this point with misaligned sprockets but the front output shaft engaged. When the shift cam turns from AWD to either 4WD modes, the sprockets appear to want to line up, but I think it's impossible to manually simulate the actions of case when it's on a bench being assembled. The coil seems to be integral to the operation, as does the need to put the case halves together. Since I have the body off, I can't even plug in everything and test it without finishing all my work, either. I'm thinking that perhaps the coil is normally energized, disengaging the clutch and preventing the misalignment from being an issue, but it just doesn't make sense to me.
If anyone has experience with a Borg-Warner 4406 T.O.D. (Torque On Demand) transfer case, I'd sure appreciate some knowledge transfer! I'm just going to put this Expedition back together and carefully test it on my lift before driving it so that I keep any damage to a minimum. I may have to remove the transfer case again before I'm done, but from the bottom this time...