Today my husband, myself, and our two little girls were walking in the woods and happened to be near some train tracks and were lucky to have a train pass by.
It was a very long train freighting coal. It had to deliver the coal up-track from where we were and so it stopped and would unload for a bit, then start up again, move a few hundred feet or so and stop again, repeat. We were absolutely amazed and thrilled because everytime the train started or stopped moving - the cars engaging/disengaging would create this unique “wave” of clankings that built upon itself and (we were at the end) left us awestruck as it traveled down the cars! We were very excited to learn that trains did this! We are curious as to what this phenomenon is called? Does the sound have a term or name? Does anyone have a recording of it?
You were listening to “slack action”. The steel couplers between cars have small tolerances in the castings that allow them to couple and uncouple without binding. When the cars push together, the gaps close in one direction, and when the cars try to pull apart, the gaps close in the other direction. The sound is created when the steel couplings bang into each other.
In addition cars have resilient “draft gear” – the assembly that connects the coupler shaft to the body of the car – that allow a small amount of motion each way to cushion the shock as the couplings go from compression to tension or vice versa. This creates additional slack and amplifies the noise when the cars move.
It’s called ‘slack action’. You heard the slack ‘run-in’ when the train stopped and cars bunched together. Then as the train started up again the slack “ran-out” as the cars were pulled apart. This is caused by the gap in couplers being larger than the knuckle that “fits” inside.
See if this helps you to visualize what is going on. Form two "C"s with your hands, facing opposite directions as viewed from above. Move them together so that your fingers of one hand brush past the fingers of the other hands and bump into your thumbs. Push your hands together and pull them apart and you’ll see how the sound is created.
Another way to think about it is to put a chain or chain link necklace on the floor/ground and pull one end of it until it all becomes one motion. Think of each link as a train car. This is just another way to explain it, I know the noise you are talking about, and hear it quite often.
That is a neat sound, one of the reasons I used to like to take pics at BN’s Northtown Yard was that from the bridge going across the yard you would have strings of cars being dragged out of one part of the yard which would stop underneath you with the resulting slack-action sound, then would start forward again as the cars were switched onto the hump track.
Slack is always fun, but it has nasty consequences. http://railpictures.net/viewphoto.php?id=188464&nseq=2
If a locomotive pulls too quickly on a heavy train, this is the best thing you could hope for.
If you’re ever around a rail yard, you’ll always hear slack action.
It’s really impressive if it’s a train of empty hoppers - it’s not “clank-clank-clank”, it’s “BOOM-BOOM-BOOM.”
I remember a train stopped in my hometown years ago. Looking back, it appears they may well have been stuck, as the slack action occured several times in opposite directions.
I’m not sure how common it is today, but at one time, especially in the days of the friction bearings (vs today’s roller bearings), a train was started one car at a time. The train would be stopped bunched, then when starting forward the locomotives only had to start one car moving at a time, albeit for a few short inches. Total slack action on a long train is measured in feet - one of the major reasons cabeese disappeared.
Friction bearings rely on a thin coat of oil between the bushing and the axle - if a car sits long enough the oil is squeezed out, leaving metal to metal contact. Once the axle makes a revolution or two the oil is restored, but it’s still a job to start that initial movement.
Interesting that you should be able to “walk in the woods” and be so close to a coal-dumping operation. The grade of the trackage where you are must be fairly level, or you wouldn’t be getting slack action with every move.
You’d be really impressed by the dumping itself–how they unload one or two cars at a time by turning them over, without uncoupling them.
Empty hoppers, I’ll try to record some that happen around here, I live at the northern end of the PRB (Powder River Basin) -For those who started the thread in case they didn’t know, or whoever- you want to talk about slack action. WOW! I have heard some bad ones, empty bethgons -coal cars- There was one about 3 months ago that knocked a picture off a wall in my house… BANG!!! Then, the ripple effect, clack, clank, clank, clank, then BANG!!! again. I’ve seen it happen on loaded trains knock clumps of coal out of cars, normally toward the end near the helpers when they start shoving to get up to the top of Parkman Pass. What an interesting sound to wake up to a 3:45 AM.
European freight cars – at least of my memory in the 1980s – had little or no slack between them. They used pin connectors between cars but featured standard-height bumper plates about halfway up the height of the car (those little round discs, two to each end of the car). OTOH, as others have said, American freight cars are all about slack.
That’s why in the USA, if a coal train makes a fairly fast stop, you’ll hear “Screeeeee, Bang! BumpBumpBumpBumpBumpBump…” (up to the number of cars.)
In Germany, though, it’s more like “Screeeeeee, BANG!” IIRC, the New York City subways, at least when periods of less than precise maintenance, also have that “Screee-BANG” sound.
And–and-- Is it true or an urban rail myth, that in steam days, locomotives pulling up slack could actually be moving at a good rate before the caboose moved, true or false. and by the way, what a great question.
That is true but only to an extent. It depends, as you can probably see, on the number of run-in coupler pairs. A mile long train will permit the engine to pick up a bit of speed (although it won’t ever be much because it keeps getting jerked by repeated slack take-ups each time a coupler pair runs out, plus the weight/drag of the portion of the train now in motion increases commensurately) by the time the last coupler pair have run out. Keep in mind that a steamer was known to spin its drivers when its weight became insufficient to keep adhesion for a given throttle setting. So, it’s not as if the hogger could yank back on the throttle and expect a nice smooth acceleration while all those couplers back down the line did their noisy thing.
I’ve got no idea what kind of slack was in the draft gear back in the day, but for sake of argument, let’s say it’s a foot between each pair of cars. That would mean that the locomotive would theoretically travel 100 feet before the caboose moved. It won’t get going very fast in that distance.
Even so, zero to even 5 mph in a split second isn’t a pleasant experience.
Welcome! [#welcome] It appears there is no stock term for the movements and reactions you describe; apparently it’s not as cut and dried as “clickety-clack.” Then again, someone may pop up who does know or remember such an onomatpoetic term.
I’d like you to note in this getting-acquainted period, that Kalmbach publishes a number of magazines for various aspects of real-life and scale-model railroading. MODEL RAILROADING is probably the busiest post of all TRAINS sites; GARDEN RAILROADING specializes in the larger one that can be operated out-of-door. CLASSIC TOY TRAINS, covers what is says; and CLASSIC TRAINS describes itself as “[c]overing the railroad scene from the late 1920s to the late 1970s, . . . [a] … forum section in everything from giant steam locomotives and colorful streamliners, to the dieselization-era.” It’s a quarterly release and wonderfully illustrated.
So don’t be a stranger! Although tiffs occasionally erupt, I thin
It is interesting that, from onboard a diesel pulling out the slack in starting a long train, it does not feel like a perfect series of little jerks, but rather like a series of surge-like resistance impulses that are not equal-spaced, nor of equal intensity. And they feel quite soft and springy, which belies the rhythmic, metallic clamor heard outside along the train. I found that I can perfectly mimic the feel of pulling out the slack on a long train in driving a car with an automatic transmission.
I think it is accurate that steam locomotives tended to rely on utilizing the slack action to start trains one car at a time. If I am not mistaken, the force it takes to break the inertia and start a standing car moving is higher than the force that is needed to keep it moving, at least in the relatively slow speed range immediately following the startup.
The total train pulling resistance slowly builds as each car is sequentially started, but the ones that have started and have their slack stretched have collectively acquired momentum from the investment of their individual starting force, and that momentum benefits starting each succeeding car.
Compared to diesel locomotives, steam locomotives are fundamentally unable to express as much of their horsepower as tractive effort at low speed or starting. So the need to take slack for starting ended with dieselization.
