Due to a very old design, the springing position in front of post permits a large change in the pulling position as load is increased. Combined with a very large play in knuckle produces an extremely large difference between the maximum pulling and pushing positions.
NOTE: Since springing is very light, exact repetitive, box mounted measurements are almost impossible to attain. The knuckles upset at the slightest touch and position is hard to judge, even under high magnification. At best results are only indicative and not absolute.
Input data is from MEASURING COUPLERS .
In the drawing below, all 3 positions are on the same mounting center. The light dashed blue lines between boxes are the screw OD; while the yellow lines inside, are the box mounting hole OD showing the .003" adjustment play. The light white are the post OD. Inside the shank, the dashed blue are the shank mounting hole OD, which changes position during pulling. The upper heads show the pulling face, while the lower, shorter head shows the pushing length.
Note: Adjust brightness and contrast for optimum viewing.
3 CONDITIONS OF KADEE 711
Maximum pull
Neutral Center, no pull. Spring pushes back.
Push
In maximum pull the PF-MC = .360", neutral = .346" and push = .329". From neutral to max = .014" = 1.22" and to push = .017"= 1.48" for a total of .031" = 2.70".
While pulling in a train, separation, compared to neutral, could increase up to 2.44" between pairs of cars, dependent on load due to position. On down hill runs all cars would bunch to a -2.96" distance. With a poorly running locomotive spacing could pinpong 5.4", resembling an inchworm.
It is quite evident the design needs revision. Still using the scissors action, the newer Micro-Trains N scale coupler has the spring in front of stud, which reduces the pulling slack. With the same action, the Accumate Proto uses cast-on side springs, reducing post play to .0025" for a total slack of .0115 = 1.001". Large slack causes problems when pushing close coupled cars. Reducing excessive knuckle play might decrease compatibility with other couplers.
For an application analysis see IHC OLDTIME WORK CAR EVALUATION.
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