This happened to me a few months ago and luckily it happened after I got off the freeway, if it had happened there I might not be here to relay this to ya:
This is a copy of my post I made on another forums:
I made a few phone calls to Dodge and also a Rear End Specialist that was recommended to me.
The call to Dodge pissed me off, wanted $1600 to 1800 and that's if no gears are needed.. Rip Off!
The Specialists quoted me at approx $610 for Pinion Bearing and also ALL bearings and clutch pack - way to go since they do have approx 107k miles.
You may want to make a note of this and if you have not changed it do it - it could happen - The Pinion Nut that holds the driveshaft is NOT
Cross Threaded. The specialists told me that Dodge has their heads up their posteriors about this. If they had used this type of nut in the first place it would have never fallen off!
Below are 3 linked pictures because the size is too large to post and I'm not sure if my comp will shut down at any time so I can't edit them
The guys at the rear end shop told me this not an uncommon and it happens to Dodges more than any other make. As I said above, Dodge does not use a compressed or cross threaded nut nor thread locking compound on the pinion shaft and this is why mine came off. After they removed the inner parts of the diff I could see that there was not one single bit of thread lock on it and that the nut had no compression marks on it at all. The new nut was slightly compressed and they used a ton of lock tight as well. The repair shop did an outstanding job and it only took them a total of 1 hour to replace the ring and pinion gear and all the clutch packs.