The shaft probably has been bent from knocking around prior to stopping the D. I would suggest contacting a local drive line shop and have a new shaft made up and install it instead as you will have all sorts of balance problems with the old one.

 

So OK I did research well all I need is a but that secures the flange yoke to the differential but I don't know where to find one. Went to a local pull your parts junk yard. Well maintained and organized one. No way to remove it. Certainly will need a bigger socket. Does anyone know where to buy a brand new nut? Or a yoke that comes with it? For a 99 Durango 5.9 v8 4wd

 

If you lost the yoke nut, your in for a lot more problems. They don't just fall off. You should find out what else is going on. Is it the 9.25" rear end?

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If you lost the flange nut you may have bearing damage in the diff that would need to be addressed also as that is what sets the pinion bearings in the diff. With the flange nut loosening the pinion is allowed to move in and out affecting the gears themselves and the pinion bearings.

 

How do I figure out the rear end size? And what you're saying could mean a thousand dollar repair?

 

As pointed out above, the nut doesn't just hold the yoke on; it sets the bearing preload by crushing a collapsible spacer and holds the pinion in alignment.. If that nut comes off while things are spinning, the pinion is free to float which can make quite a mess.

IIRC the 8.25 has 10 cover bolts and the 9.25 has 12 ..

...tom

 

Buy the whole rear end of the unit you looked at, But you'll also need to pay attention to ring gear size on replacement unit, it will need to match your front ring gear, if you use 4wd...

I think it'll be much simpler to change out rear than to open diff up and replace guts! Typical gear sizes from 99's are 3.55, 3.92 a metal tag should be on one of the diff cover bolts or a plastic tag around driverside axle tube.

 

Sounds like pinion bearing failure...which means the rear end is toast.
You should be able to find a used rear end for around $400. You're looking at about a $1K bill all done having a shop replace or rebuild the rear.
If it occurred at low speeds, the driveshaft should be ok with a rebalance.