@SDBOB1 posted:One weaver box car for some reason the plastic floor was bowing down. So I made a whole new floor out of sheet steel. Runs fine.Discarded plastic floor.Couldnt figure out why it bowed down.
SDBOB1, Weaver made flat, rectangular steel weights for some of their boxcars that were attached with a single bolt and nut. They were mounted in the center of the car floor...exactly where you DON'T want to put weights! Over time, the plastic floors/frames on some (but not all) of these cars sagged in the middle...no big surprise.
This is only a guess, but the car you're talking about may have had one of these center weights installed at some point. Did you buy it new? One of the telltale signs is a hole drilled in the dead center of the car floor where the bolt went through.
The added weight really needs to be positioned over the trucks, especially on any boxcar with an all-plastic floor and sub-frame. The photo below shows two Weaver boxcar floors with stick-on wheel weights that I added to bring the car up to NMRA standard. You can also see the hole drilled in the center for the Weaver weight.
And here's a photo of two Weaver boxcar floors with no center hole...
