Although I had just finished these cars, a few days later my order of the new Sergent Engineering S-scale couplers came in the mail. You can read more about the couplers themselves in my Sergent article, but this brief article describes what I had to do to get those couplers installed. Until their arrival, my fleet standard had been the Walthers HO-scale ProtoMax coupler. The ProtoMax draft gear box is not compatible with the S-scale Sergent coupler, so I decided to use some spare Kadee S-scale draft gear boxes, which, as you can see in the photo below, is a perfect fit.
So, I first had to remove the Walthers couplers. In my January 2013 article on this car's construction I mentioned that it wouldn't be too difficult removing the coupler. Well, I was wrong. The glue really held them in place. This is good, of course, but not trivial to work on now. The Kadee box is wider than the Walthers one, so I had to remove more material from the end sills.
The Walthers box is also longer, but rather than removing part of the center sill, and the lead shot balls that are very firmly glued in place, I decided to just make the draft gear box shorter. That has no impact on the functionality of the coupler (since it doesn't use a centering spring). I then used 5-minute epoxy to glue the coupler to the body.
A quick check on my coupler height gauge verified that it is installed at the correct height (the top of the coupler is supposed to line up with the top of the wooden block). Sorry for the blurry photo, but you get the idea.
And here is the result. A coupler that is perfectly to scale. I will paint and weather it later.