So I've noticed a trend among 110, 112, 120, 140, 300, 312, 314, 316k, and 317 seats. It's mainly among the smooth seats, but also can occur in even new seats and fender pans, such as the fenders for the 316, 318, 322, 330, and 332.
It's an issue on all tractors, but so much worse on 120 and 140 because of the longer seat springs.
The issue is that some genius designer over at deere decided it would be a good idea to essentially mount the seat on 2 stilts with 8 toothpicks, with the springs being the stilts and the bolts being the toothpicks, and the glass being the fenders when they crack and break the mounting bolts off.
Below I have analyzed it, and I think I've got down what causes the issue.
Front view, with no forces applied. Everything is fine. No cracking occurs.
The issue arises when you apply a sideways load to the seat, such as sitting on it, or mowing on a hill. This causes huge stresses which, because of deere's genius design, lead to cracking.
When you apply a load to the side of the seat (one spring only), the forces are similar, leading to slightly less stresses, but still a lot. cracking occurs, but slower.
From the side isn't much better.
When you apply a load to the back, it provides some... Subpar results. You'd think it'd be fine, but no.
Applying a front load is a tiny bit better, but it's still an issue.
There's a couple fixes.
1. Widen the springs. Pretty difficult, probably not the best option.
2. Weld 2 bars between the springs. This essentially makes the springs one assembly, and also spreads out the load and keeps them from twisting as much. This mainly helps because the springs twist not because they're too thin, it's because the materials they mount to is too thin.
3.Add seat suspension. Even making your own is better than the stock springs because of how skinny they are and how tall they are.
I'll also add a reply comparing seat suspension.