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[quote user="BaltACD"] [quote user="GM1361"] What is taking slack in the following sentence? CAUTION: Taking slack is not a recommended method for starting a heavy train on a heavy grade. Short brake release times will release the brakes on the entire train, and the rearportion will begin rolling backward while the head portion is starting forward, easily causing a train separation. <div style="clear:both;"></div> [/quote] Couplings between cars have some 'slack' in them - potentially on the order of 1/2 inch to a inch per coupleing + the movement of the draft gear on each end of the car.  As train lengths increase, the amout of 'free moving' slack in the train also increases.  Improperly controlled slack action is the primary cause of shattered coupler knuckles and pulled out draft gear. The action described in the 'CAUTION' is a situation where the entire train is stopped on a ascending grade.  The engineer has 'bunched' the slack in the train, so that each coupling has the maximum slack distance to move before starting to pull on the car behind it.  In the procedure being cautioned, the air brakes are applied on the entire train.  As the engineer begins to start the train, adding power to the locomotive consist, he is also releasing the air brakes - pulling the slack out and starting each car individually from front to rear.  The caution refers to the fact that the brakes will release on the rear of the train before the starting secquence of pulling out the slack has gotten to the rear of the train.  Gravity will have the entire portion of the rear of the train pull against the starting head end of the train as a 'solid unit' with a much higher draft force than the engineer intends with his starting sequence.  The high draft force is easily capable of shattering a coupler knuckle or finding the weakest draft gear, thus stopping the train and necessitating additional actions being taken. [/quote] Very informative response!  What is the total distance a freight car will move before it begins to pull the car behind it?  Someone told me years ago that it was in the neighborhood of six inches, i.e. three inches for each car.  I have no idea whether he knew what he was talking about.
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