Besides my 04 F350, I have a 75 GMC pickup that my great uncle had purchased new. It has 55,000 original miles on it, and is in very good shape for its age.
The front diff was leaking a little around the cover, so I decided to service both pumpkins. I started with the front. When I pulled the cover, it looked like there was a sludge covering the ring gear- that was the first impression. It didn't take long to realize that my eyes were deceiving me- it wasn't sludge, but weld. At some point, the ring gear has been welded, completely, to the differential. All of the bolt heads were broken off, with the bolts still in the gear. There were also some chunks out of the ring gear teeth, and the inside of the cover was chewed up.
The wear patterns look great, and there is no damage to the pinion. The axle runs great- I never would have realized that it was damaged and hobbled together.
I'm not going to do anything. I cleaned the cover and put it back, let the silicone set up, and filled it. I would like to know, though, what happened. His son, who I got the truck from, has no idea. Anybody with a solid, educated guess?

 

maybe someone re geared the truck and did not torque the ring gear bolts. over time the bolts loosened up and broke.
your uncle, being a practical old timer that did not "waste money" on repairs he could do himself, welded the ring gear to the differential because he did not have the time or resources to take it apart and replace the bolts.

 

I don't believe that it was regeared. But, thinking through the broken two broken teeth on the outer edges (about the size of a pinky nail) and the damage inside the cover, I think something got churned up. About the only thing could be the ring gear bolts- maybe one or more had backed out.

I do agree with the "Practical old timer" and "not waste money"- that was uncle Jack, to a T. They obviously pulled the diff to weld it, but he wasn't about to buy new parts.
It is a pretty amazing repair- it is true and isn't causing any abnormal wear. They must have taken their time welding it, to keep the ring gear or plate from warping.
It is also under constant load- this is a full-time 4WD/NP203.
Uncle Jack may have been tight, but he didn't abuse his truck. So, I do concure and believe that something came loose, not broke from abuse.

 

i serviced the rear axle this morning- the cover hadn't been off in 40 years! It still had the original gasket, and there was very little gear oil in it. It was also thick, but there was no water.
I cleaned things up, put the cover back on, filled it up, and then watched oil pour out of the pinion seal. That's why the level was low. I will put a new seal in tomorrow morning.

 

I've heard of people welding the spiders up, is this along those lines?

 

no. welding the spiders locks the diff so both axles spin the same all the time: think a spool used in drag racing.