1811 Steering assembly -- what kind of force would break this ?

[Gregory]

Bought an 1811 a few years ago. Once I fixed the fuel issue that tractor ran for 3 years without a problem. My son was mowing a neighbor's yard, made a turn and the steering snapped, according to him.

When I looked at it, the steering wheel would spin freely without resistance, but the wheels didn't turn. Had to load on a trailer to get home. Once started to inspect, I found the problem....... Initial survey showed that the pivot plate moved and flopped freely with the steering system still fastened to the frame. After removing the gas tank I discovered something I've never seen before. Don't think normal use would cause this and there where no indications other than the normal slight play in the steering which I attributed to normal spindle and tie rod end wear.

Brief history, I purchased this from a dealer a few years back, everything worked as it was suppose to and was told this had come as a trade-in from a commercial contractor. Now I have ordered a replacement steering assembly which I'll get later this week. I don't believe that this is a common problem and these housing are robust with both upper and lower bearings, but what the heck could have caused the housing the split apart ?