Last weekend dug a drainage trench, with the 931B/backhoe, about 400 to 500' long and was lucky the ground wasn't too frozen with the mild weather we've been having. I had one spot where it was but went back in the trench and changed direction a bit and it was easier digging. Today I went out and did some rather minor digging and noticed something happened to one of the stabilizers. I got off and took a closer look. The pivot frame on one side ripped right off from around the bushing. I could see a couple small spots where there was a fresh break in the weld but around the rest of the weld appeared to be rusted so I think it may have been developing for some time. I think that the Cat welding procedure contributed to the failure because a few years ago the top plate of the swing post ripped off and cracked all the way around the outside edge of the weld. The break today left a little weld on the plate but I wonder if putting a hot fast weld in without any preheat may have had a bit of a quenching effect on the steel. Thankfully I was able to lift the stabilizer and get the machine back inside my new pole shed. Now I'll have to get the welder running again and fix it but I don't know if I want to do it in the cold. I guess I'll see what the weather does. Cat didn't put much reinforcement around where bushings are welded. They cut a hole in the plate to put the cross bushing for the stabilizer but there's only about a 1/4"-3/8" of meat around it and it just ripped right off. The plate looks to be 1/2" so you'd think they go at least the plate thickness. I'll put a bevel on it when I weld it so it will have some extra reinforcement and penetration. At least it's not as bad as the swing post ripping off but still a pain in the butt to have fix it.
Most of the accessories for Cat and a few others are made overseas, much of which I don't care for as to quality of work. Been looking to replace my old Allis crawler loader with a decent excavator I can get more work from but I see the same issues over and over with re-welds over the OE welds, fish plates over cracks due to poor weld techniques or poor choice welding style(IE mig over tig or GMAW), mig is fastest and easiest for factory work but poor penetration in most cases. I prefer stick for most field work, tig for in shop as it penetrates better and makes a cleaner weld if prepped and performed properly.
I think the backhoe is made by Cat in Japan but just not enough meat in a few high stress area's. The top plate for the swing post was 1" thick but then they put a 1/8" NPT grease fitting through the middle at the narrowest point around the bushing and that's where the crack started and then followed all the around the outside of the weld where there was slight undercut in a couple spots. They could have easily put more meat around the bushing pivots on the stabilizer. Why not make it so the welds hold everything together but the design has strength without relying so much on the welds.
Sorry to say the 70's Allis I have is far ahead of that game as to strain relief at critical points as you noted for the grease fitting. They actually thought of that 50 years ago welding bushings or extra strain plates or affixed strain relieving fixtures to the machinery. Expensive in the short term, worth every penny down the road.