Jeffzirlin; Diagnosing by sound like you did on a drive line can fool someone into thinking that what they are hearing is right near where they had the rod and it doesn't have to be. Most things that can go wrong in a differential will be frequency and or load indicated, it will get louder or vibrate in amplitude or make more or less sound amplitude with speed, frequency, changes. There are a few things internally in the differential that can but are not common that can cause it to suddenly bang with acceleration or deceleration. Like the other posters wrote above I recommend that you don't jump to conclusions about it, take the drive line slip joint apart and grease it first. If you have difficulty with that dont even consider trying to rebuild your differential which I think is an 8 out of 10 difficulty job. I doubt that it would be a bad drive line center bearing or it would roar all the time just change amplitude with speed. Check for loose parts everywhere if you have not already. Assuming that you have a Sterling 10.5 inch differential if it is the internal parts of the units differential it doesn't have to be the ring and pinion alone there are several other things internally that can cause what some would call a banging noise. Drop the inspection pan on the differential and take a look, might be something you see easliy that takes the mystery diagnostics out of it. Rebuilding one of these rear gear sets is something most dealers don't do correctly and like RT suggested above some drive line businesses don't do correctly either. It is not just the pinion shaft crush sleeve washer alone that is difficult to adjust and may take several tear downs to get it correctly set up it is the ring to pinion engagement on axis, there is a washer adjustment for that between the larger pinion bearing and the pinion gear, that one alone can take a couple of adjustment cycles - on-off-adjust-assemble. There is also the ring gear adjustment perpendicular to the pinion for lash and engagement that is done with large shim washers behind the differentials two side carrier bearings. It all has to work together to be "correct" More put together-take apart-adjust and start over cycles. Most dealers will just slap it together and if it doesn't make noise right away then they let it go, they are not going to fine tune it, they don't do many and can't tie someone up on it that long.
Is it worth it you wrote, well that is subjective. Money wise the rebuild parts alone will likely cost you $1000 bucks, Maybe a little less if you bargain search. You will need a place to work on it, tools, jacks, torque wrenches, a press, one or dial indicators, a 0-1 inch outside micrometer and a very strong back to work under the truck unless you have a lift. You will have to be creative in building something to get the bearing outside races in their fits. Dealers, look to pay 1000 and up plus parts cost to get a complete rebuild and you get what you get. Drive line shops depends on the shop.
So, look around and try the simple stuff first. That I know is worth it. Good luck, 106
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