I think the main parameter of interest out of those that I posted is RDU_MTR_POS. I believe the magnitude of that value corresponds to the clutch engagement in the RDU. I highly recommend forscan, lots of tutorials out there. It is a great diagnostic tool for nuanced issues like this one.
It is interesting that the TCU relearn fixed yours. I don't think the TCU has any direct control over the RDU. Only the AWD module should. Now those two modules certainly communicate and I am sure there are programmed dependencies between them during operation. I only performed the AWD module adaptive learn reset.
Since you are going the warranty route I would just stay on the dealer and try to get a resolution. You can also work with the ford account on this forum to get a case number opened up. I doubt getting a case number opened helps very much. In my experience in the past it does absolutely nothing. The squeaky wheel gets the grease!
My bad, I did the AWD relearn too. Mine felt like a small clunk when downshifting, usually worse when cold. I'll drive it a bit longer to see if it comes back.
Issue is not related to anything in the vehicle or in the bed. I removed everything from the truck initially to rule that out. I usually keep quite a few emergency items under the rear seat and was thinking along the same lines as you.
In my experience the fluid change did nothing. However, I am glad I changed the factory fluid out. The drain plug magnet had a lot of magnetic fuzz on it. No shavings large enough to feel in your hand. Just break in material more than likely. I had also heard rumors of under-filled PTUs and RDUs from the factory. Couldn't sleep at night until I knew that they were properly filled hahaha.
I am leaning towards the RDU, reasoning detailed below:
I feel like I need to add some additional information to the pictures above. As mentioned previously I think the main PID of interest here is RDU_MTR_POS. It is the PID that changed drastically after the AWD module adaptive learn reset. The pink and yellow lines also appeared to be different. However, after additional testing today those lines track inferred and requested torque. They really only start to pickup when the RDU has actual load applied to it during acceleration or sitting still in drive with torque applied to the RDU and the RDU clutch engaged. They do not start picking up during deceleration even with the RDU clutch engaged. I believe the varying results on those two traces is a result of me not coming to a complete stop during testing or coming to a quicker/slower stop.I checked under the truck and everything is secure, no suspension movement anywhere, driveshaft and half shafts felt solid at the RDU. So I went and hooked up forscan and got it to clunk immediately. It happens right at 16mph only while decelerating. See attached forscan images of PTU and RDU PIDs. The first picture is an event capture during a clunk. The second picture is the list of PIDs and the order they are plotted, see summary below as well.
-PTU_CLTCH_CMD
-RDU_CLTCH_OPEN
-RDU_MTRPOS_KISS
-RDU_MTR_POS
-RDU_TRQCAP_INF
-RDU_TRQ_REQ
-ROM_CHECK_AWD
The third, fourth, and fifth pictures are event captures without a clunk after performing an AWD module adaptive learning reset. I figured I would try an adaptation reset on that module to see if it would clear up the clunk or at least change it to further confirm my theory of the RDU being the issue or related to the issue. Had good results with cleaning up clunky shifting on an F150 with the notorious 10 speed. Sure enough it drives completely normal again. I exported those recordings to a csv file and will do some more detailed analysis tomorrow. Will report back with additional information and if the clunk seems to be gone still.
Could you share how to perform the AWD module adaptive learning reset? My thud is worse than ever after Ford did the TSB and changed the oil in the RDU, which by the way did have metal shavings in it. The truck also revs up now after each thud. Lovely!
