Freight car coupler problem - need help

If it's a molded plastic truck, you can spread the plastic side frames apart at the axle to allow removal of the wheel/axle assembly.  If it's a die-cast metal truck with the side frames mechanically pressed to the bolster, then there is practically no way to remove the axles without destroying the truck.

The easiest way to fix your dilemma, for either die-cast or plastic truck, is to simply double-wrap a small rubber band around the coupler shank and metal pin arm.  I bought a package or cheap black plastic bands at a dollar store that work great for this.  Young gals like to use them to tie their hair in ponytails, so you would most likely find them in the hair care section of the store.  As small as they are, these plastic bands can stretch a crazy amount before they break.

Once you have secured the uncoupling pin to the coupler shank with a plastic band, most likely you won't be able to use it over an uncoupling magnet due to the stronger tension of the band, but at least the knuckle will stay shut.

Clearly from the picture, it's a diecast truck.

Those trucks don't come apart easily, so you have to do your bending with the axle in the way.

I had to do that to a coupler on my pwc caboose once. You could try gently and carefully bending it with a pair of needle nose pliers. Just a little tweak, not too much, and that seemed to do the trick for me.

Went with the needle nose plier approach without attempting to remove the axle.  Didn’t take much and everything works great now.  Thanks to all.

Seems like a bit of a quality control issue as I’ve experienced this once before with a new car, as well as have seen similar posts.

My daughter had braces, she extra rubber bands, I have used those a few times when i needed to.