Well, actually it’s a grade problem, the couplers are fine 
Anyway, exiting a truss bridge, the cars uncouple from my engine just as the engine is going down the grade.
Obviously, the grade is to steep, but that can’t be dealt with for now. The couplers barely offset enough to uncouple.
Can I shim one of the couplers to compensate for now, or is there some other fix(es) besides changing the grade (which isn’t an option for now…in the future) ?
is it only happening where the cars meet the engine? If so try finding a thicker coupler may look littels less realistic but until u can manage the grade this should work. And and another way to fix the grade without tearing it up find the on point on disconnection and there try to make it a smoother grade . Or another way is to make it one piece of track such as flex track then it will be smoother on the downhill grade
Yep, only happening to the first car after the engine. I.e., the other cars all stay connected to each other.
Thanks for the info; I’ll try looking for a thicker coupler. I’ll be taking this layout apart after this summer anyway, but need to have it accesible until then.
glad to help i too had the problem but it occured in the early stages on building hte grade so i had no problems fixing this issue but it was a littel annoying
If the problem is happening at the top or bottom of the grade, then it is not so much the steepness of the grade that is causing the problem, but the sudden transition from flat to grade. A long rigid loco starts down the slope causing the rear coupler to lift and disconnect from the following car. The freight cars are likely shorter, so the coupler lift is not so marked and the cars don’t un-couple. If you had longer cars or even passenger cars, you may well see the same problem. Going up the grade the rear coupler of the loco tends to drop relative to the first freight car coupler.
The way to cure this is to have an easement grade. Essentially you want the transition from flat to grade to start gently and then gradually increase in grade to the maximum slope. The same applies for the up slope. If you could view a section along the track you would observe a gentle S shape. If the easement into the grade is gentle enough you can eliminate the problems.
This is exactly what is happening; the lock starts the descent, but the cars behind are still on the flat, etc.
Long cars, short cards, no difference.
The loco isn’t even that long (only a four axle), but it’s long enough I guess What’s even more strange is that an F unit loco the exact same length, etc. doesn’t do this.
are the couplers the same?
My LHS suggested Kaydee shelf couplers. They solved my problem, similar to yours, a sharp break in grade that my spectrum passanger cars didn’t like.
Yep. Arthill, thanks for the tip, I’ll look into that.