Is there a maximum train length?


I recently had the pleasure of operating on a layout with Sergent Engineering couplers. I liked them enough that I thought I would give the kits a try. I happen to belong to a modular model railroad club and we sometimes run scale mile or longer trains. My questions: Is there a maximum train length for these couplers, and has anyone had a coupler open due to excessive force? From what I observed on the layout I operated, it appears that there will be no issues.


Dave Snyder

Hi Andrew, I have been using Sergent couplers for about 10 years and have not had a coupler fracture, but occasionally I get an uncoupling that I attribute to a track geometry/harmonics phenomenon. If it repeats, I simply
turn one car around or move the car in the lineup and that usually remedies the problem. I did drop a car once and it landed on the coupler, didn't damage the coupler, but the pocket(s) had to be replaced and I changed it to the Accurail scale pockets. It looked better anyway and the coupler worked fine. Although I only occasionally run a long train, the track geometry/harmonics happens on shorter trains as well, although it is rare in either case.

Dave Snyder
Louisville, Ky.

Alan Hummel


Early on after Frank die cast his E coupler,the question of strength came out-this was at least 2009. A couple of modelers tied a cement block to a coupler somehow as I remember,& the Sergent didn't fail.

I plan on 20 car trains,maybe 25 as I have Atlas diesels & that's what I was told an engine could pull per unit not in lash ups. So I figure I'm ok,but I have to remember,even if a knuckle fails,it happens on the prototype as nothing is 100%.

Your question is a good one & the answer might still be listed under,"Frequently Asked Questions," at the Sergent home page.

Hope this helps.

Al Hummel

James Wall

I have experienced on failure of Sergent type E. I have a forty car train of the old Roundhouse Ortner 5 bay hoppers that are weighted to about 12 ounces, give or take. On my 2.5% incline with One Kato SD45 and two Kato SD40-2’s pulling and two Atlas SD24’s(new version) in helper service on the end, the train crested and some slacked. When the slack was taken up the coupler between the two SD24’s broke the shank.

When I took the coupler piece out of the loco I examined it and it looked bent. I am sure this loco took a hit some time or the coupler shank was bent when I installed it without seeing it.
This coupler would have come from some of the earliest Sergents, like right after Frank started.

I would not be to concerned about a 20 to 25 car train. My cars are weighted to way above NMRA standards, so this train by my rough math is something like 30 pounds in just the cars.

James Wall
Rural Hall, NC