It is surprising how much "slack" there is in the knuckles (couplers), The longer the train, more cars, the more slack. So when the train brakes the cars push forward towards the front. If the engineer is not careful when accelerating and takes up the slack too fast then it could blow a knuckle, especially towards the rear. This is even more true in winter weather when the knuckles can be much more brittle.Watching a lot of YouTube vids on trains I’ve picked up some of the lingo they use. I had heard that term before “Slack”. I didn’t realize just how much is involved in getting these things up to speed and how much braking/acceleration affects the whole train,front to back.
One of the things I found out is why sometimes you see 3 engines at the front with one or 2 facing backwards. I always thought it was for torque reasons. Lol. It’s so they don’t have to utilize a turntable when the engine returns from the direction it came from. The lead engine usually carries on somewhere else. I’m sure there’s other reasons but that’s one of them I’ve seen on a vid.
And who gets to change a knuckle? Why the trainman who now is up front with the engineer. He gets to sling one over his shoulder and trudge back to change it out no doubt wondering about the competance of the engineer.