Hard to tell from the photo, but it looks like the crack isn't shiny. With the paint & other surface rust on there you'd need a much closer photo. A bit if rust on the crack surfaces indicates it's been there a while.Those cracks don't really have to do with the jack even though they are lined up with it... it all has to do with the stress concentration at the end of the weld on the tongue, the cracks on both sides line up with the end of the welds... It sucks but if you have a welder not a big deal, it looks like it's been around the block for a while, it happens... At least he obviously had tongue weight so you still have a trailer and neighbor! trailer sway sucks and can get bad... I've literally been towing, couldn't move the load forward and bought tongue weight...
I'm thinking metal fatigue over the years that opened up gradually and became more visible after the last haul. It doesn't look like anything sudden.Hard to tell from the photo, but it looks like the crack isn't shiny. With the paint & other surface rust on there you'd need a much closer photo. A bit if rust on the crack surfaces indicates it's been there a while.
Somewhat back on thread topic:
And back to the regular presentation of those in humanity to beware of.....
Broke a long standing rule of mine and loaned out a trailor and got this back. As expected the guy had no idea how he loaded so much for the crack to happen. It’s kind of in line with the jack.
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Curious why you went with the side mount swing back when the center mount A frame is the same price.
I have to use side mounts on mine and had to add a second one so the tongue wouldn't twist.