New dance step?
No --. We see many trains over the same tracks go back and forth and only occasionally does a train have a situation where the couplers will raise, travel a few feet and then drop.
Could this be due to switches, crossings or slack?
Why only on a few trains and not on all of them?
A “dip” in the track causes that. It may be due to a softspot in the sub-grade (below the ballast) or the ballast has settled more in one spot than in the adjacent spots. Send in the tamper to get the track smooth and level again.
It also takes some slack for it to happen also. The force applied by the draft gear trying to line back up has to exceed the coefficent of friction between the couplers. The couplers slide much easier when there is a little slack in the train. Longer cars next to short cars can make it worse.
I once rode from Chicago to Ft. Wayne and back behind N&W #611. On the way back the train was pulled backward and only the engine was turned. Those of us in the observation car were right behing the tender and had the couplers slip vertically at one point. It sounded like a cannon had gone off and just about everybody jumped up out of their seats. Guess that back coupler on the obs was a little rusty from lack of use and it took quite a variance for it to slip.
I once rode from Chicago to Ft. Wayne and back behind N&W #611. On the way back the train was pulled backward and only the engine was turned. Those of us in the observation car were right behind the tender and had the couplers slip vertically at one point. It sounded like a cannon had gone off and just about everybody jumped up out of their seats. Guess that back coupler on the obs was a little rusty from lack of use and it took quite a variance for it to slip.
Our track is far from smooth - the banging of the couplers sliding vertically is a way of life for us.
I would tend to think that the long-wheelbase cars (flats and autoracks) might tend to mask the cause of the vertical movement, as opposed to cars with a shorter wheels-to-coupler distance.
SJ, if you’re seeing this at Camp Mookie, it’s probably the condition of the grade crossing itself that causes the difference in level.
You probably don’t see it on the coal trains, unless you’re looking for it–those trains (particularly those with rotary couplers) have Type F drawbars, which prevent vertical movemnet.
Around here, I play a little game with it–if we’re watching a manifest freight at a grade crossing, we wait to see when the couplers start doing that. What it usually means in our case is that you’re getting near to the end of the train, where in-and-out slack action is more common. You won’t find the couplers moving like this through most of the first half of the train, where the slack is usually stretched.
Out here, on just about every crossing the train goes over, the couplers rise as the go reach the crossing and drop afterward. It is loud. I can dig up a video if anyone doesn’t know what that’s about.
You will also see it a lot between loads and emptys, when both have E type couplers…
Low spots, or crossings like the one one we watch at, or loose joint bars combined with slack will let the loaded car, which is sitting on compressed springs, to drop down, but the empty car will “bounce” over these spots, and cause the couplers to slide up and down.