I don’t like the slack action in Kadee’s S scale couplers, so I’ve been modifying them to remove it.
On the underside of the coupler shank, there’s a projection that fits into a slot in the coupler box to aid in centring the couplers. I slice this off and sand/file the area smooth:
There’s also a small projection at the back of the shaft. I remove this, too:
Then, instead of adding the centring spring, I cut a piece of .080″ x .080″ styrene strip and use it. I cut this so it’s just a touch shorter than the opening for the spring (minus, of course, the post in the coupler box). This prevents the coupler from sliding forwards and backwards in the box:
This means my couplers do not automatically centre. But that’s fine. With all track a reasonable reach from the front edge of the layout, I can manually line up knuckles before coupling – something that brakemen have to do on real railways on occasion. The extra time to line up couplers represents the time a brakeman would spend visually checking the alignment, pulling the pin, etc.