In a number of posts over several years, I have talked about maintaining a fleet of freight cars: my own fairly large fleet. What happens from time to time, in essence, is that cars that have been pulled off the layout for any kind of poor performance gradually accumulate until they are in the way. Then it’s time to work out the kinks and return them to service — if possible. The background here is what I call my “rookie test” for freight cars (see my description at: https://modelingthesp.blogspot.com/2018/07/the-rookie-test.html ).
The worst offenders are the cars that only misbehave occasionally. This makes you pull your hair out. But they still have to be fixed. The most common type in my experience is derailment due to misbehavior of the trucks. I postulate that occasionally a wheelset gets cocked or jammed in the sideframe, leading of course to derailment, but because this rarely happens, it’s hard to find. Simple solution: replace trucks. Here’s one of my misbehavers, shown right where it derailed
I replace lots of trucks nowadays. Back in the day, I always tried to use the kit trucks, sometimes with Kadee replacement wheelsets. Now I’m realizing that it can be the fault of the sideframes, and that replacing the truck can correct the problem. It can also be the wheelsets, if I used the kit ones, and nowadays I tend to replace with InterMountain wheelsets when they fit the sideframes.
Replacement of trucks can easily throw off the coupler height, as some manufacturers of model freight cars have designed models so that they have to be mated with the company’s own trucks. I always carefully check coupler height after truck change (for more about this, you can see my post on coupler maintenance, at: https://modelingthesp.blogspot.com/2019/10/maintaining-model-couplers.html ), and verify on the layout.
There are also problems that arise when a kit coupler arrangement is entirely replaced. Careful checking of the new coupler is essential. As always, I use the Kadee gauges, shown here with a Thomas Trains wine tank car from the 1950s:
Lastly, I have mentioned before that I also make “dynamic” checks of freight cars that have been repaired or upgraded with new couplers or trucks, deliberately pushing and pulling a group of suspect cars, often mixed with correct cars, through a sequence of turnouts (I described this process in an earlier post: https://modelingthesp.blogspot.com/2019/06/rolling-stock-upkeep.html ). The photo below shows such a test at Shumala on my layout. I continue to do that with cars that have had trucks replaced, since it was truck misbehavior that caused replacement in the first place.
A large fleet of model freight cars like mine simply requires maintenance, there’s no way around it. What works for me is to have an established procedure for this work, as I’ve described in the present and previous posts, and to stick to it whenever a batch of repairs/upgrades is being done.