Mister Roper. Im a service advisor for Ford and that's crazy story that they voided your warranty for only having and axle back. They had no base for doing so. The only thing we can do is not approve warranty filing on parts and or service that are directly affected by your aftermarket parts. The only reason we have to do that is that Ford will not pay the warranty and the shop would end up paying the costs. We have only sent in for someones warranty to be voided once. But it was an 6.0 f350 with 2 chips, propane, and nitrous injection, full exhuast, and had already had one tranny replaced under warranty. also the truck had all these website stickers on it and we found video of the same truck on the dyno and at the track. The guy wanted to fight me when he found out his trannsmission going out wasnt covered by warranty any more. but he was crazy thinking he could double stack chips and run nitrous and have a warranty still.
First off.. Roper did not deal with you so you have absolutely no reasoning to post this.
Second... you are either one service writer at a VERY RARE dealer, or completely full of shit. And considering your post count and join date, I am leaning more toward the latter.
Internet is flooded with story after story of dealerships trying to play the "void your warranty" card for just about any reason you can dream up. Hell, it is not uncommon for people to be told that a non drive train issue would not be covered under warranty because they have a CAI installed. In spite of the number of times the MMWA has been posted stating the dealerships do not have a leg to stand on unless (as you stated) the aftermarket part can be proven to be directly related to the failure. For you to claim to work at a dealership and state basically the exact thing the MMWA states is pretty hard to believe.