Get a Kadee gauge and check the coupler height -- also make sure the glad hands aren't catching on track, frogs, etc. I find them often a bit low out-of-the-box.
An “S curve” can cause problems with long passenger cars. There should be some straight track between reverse curves.
GARRY
HEARTLAND DIVISION, CB&Q RR
EVERYWHERE LOST; WE HUSTLE OUR CABOOSE FOR YOU
If you're having problems with a particular brand of car, what is it? For example, I've got some Rivarossi coaches that work fine on 18-inch curves, but a measurement error resulted in a short 17 3/4 inch curve. I had to re-do the whole half circle to get those cars to work. I replaced the original couplers with Kadee #5, and then Kadee #58. The #58s would not stay in the box and were terribly loose, resulting in a lot of uncoupling.
It takes an iron man to play with a toy iron horse.
Shelf couplers solved a similar problem for another modeler with long auto carriers uncoupling. Just saying...
Rio Grande. The Action Road - Focus 1977-1983
What radius are your curves? Long cars do not like the typical "trainset" radiuses such as 18" or 22".
Welcome to the forums.
Sharp curves, abrupt elevation changes have been mentioned as the most common causes. Even if your couplers are good quality and at proper height, do they flop up and down in the coupler box? If so, shim them to tighten them up, but be sure to maintain proper height.
Good luck,
Richard
Too-abrupt changes in elevation are very often a cause. Also too-tight curves for the equipment. What radius are you using and with what manufacturer's cars?
Layout Design GalleryLayout Design Special Interest Group
Assuming the couplers all check out at correct height using a Kadee or other coupler height gauge .... more facts are needed (which won't prevent some educated guesses of course):
Do the couplers otherwise perform mechanically? For example, do the coupler failure problems go away if you put a 40' freight car in between each passenger car? This is a form of trouble shooting.
Do you have diaphragms at the ends that tend to push the cars apart and hence can invite coupler failure? This is actually a result of too sharp curves to have diaphragms, and maybe even too sharp to have your length of cars.
Body mounted or truck mounted couplers? Body mounted couplers can be stressed if curves are too sharp. But truck mounted couplers can have a tendency to droop, resulting in mismatched coupler heights and coupler failure. The drooping is particularly noticed with light weight cars such as the old AHM and IHC cars. In fact, do the troubles do away if you put some temporary weight (e.g., your finger on the roof of the car) over the wheelsets?
What make of coupler? In my experience and the experience of others certain Kadee clones seem to fail more than others.
Where do the couplers fail - on curves, which is a common problem if curves are "too sharp," or at particular spots such as elevation changes? Sometimes subtle and even unintended elevation changes can cause sudden coupler height differences especially for long cars with body mounted couplers.
-------------
If the couplers fail repeatedly at a particular spot, set yourself down so you are at eye level to the coupler and push the cars back and forth, trying to cause a coupler failure. My hunch is that you'll see a coupler height issue due either to a subtle elevation change, or an issue with body mounted couplers.
More could be said but it would be speculation without knowing more facts.
Dave Nelson
I have a problem with long passenger cars that keep uncoupling (HO Scale). I replace some of the couplers but still i am having the same problem, need help.