Has anyone found a simple way to minimize or prevent premature opening of these late postwar couplers under load? I find that some of these couplers will open after a half dozen laps when in the middle of something like a 15-16 car freight. The spring steel retention mechanism just seem to be weak on some cars.
runtime
Runtime, I’ve become something of an expert with couplers. Most uncoupling problems basically result from pressure or shape of the armature, the shape of the knuckle pin, and the contact made between the pin and the knuckle. Uneven track or a dangling coupler button plate can also cause them.
In your case with the AAR style plastic truck (with molded Timken roller bearings). Lionel made a design alteration in both the knuckle and the spring plate piece in 1962 to lessen uncoupling problems under load. Could very well be that you have some of the pre-1962 truck sets.
There’s several ways to try and fix this. You could try giving a slight upward bend to the spring bar, so that the end pin engages more securely with the knuckle. You could also replace the knuckle with a newer Lionel one. You could wrap a small rubber band around the coupler arm. I’ve suggested small black girls hair rubber bands… you can find them at dollar stores in bags of anywhere from 200-500 for a buck. They also make for super looking loads in open gondolas.
Before you buy the black rubber bands, you could even try a nomal rubber band or a twist tie off a bread bag, just to see if that works.