One of the most frustrating parts of installing Sergent couplers is the spring that provides some friction for the coupler in the pocket. Fitting between the coupler post and a slot in the coupler, it can take a few lost springs before getting comfortable with this task.
This can be made even more teeth gnashing by coupler pockets that lack a solid "floor", as the spring wants to slide down and under the coupler into the pockets below. With their great details and construction, the Trueline trains products are desirable for a number of reasons, but alas, they lack the solid coupler picket "floor".
After trying a few different things, I've finally come up with an easy solution that may help other modelers. As I was just doing this today with some slab sided hoppers, and I had the camera nearby, I thought this might be a good opportunity.
Remove truck for access (if needed)
Remove the coupler pocket lid.
Remove the coupler.
Remove the bronze spring plate. This is a great shot of what I mean by an uneven "floor" in the coupler pocket.
Cut the side "wings" or spring section off of the bronze spring plate. Note that I've found the curved tweezers very useful in this operation (removing the old, and reinstalling the modified spring plate.
Re-install the modified bronze spring plate
insert a tested and working Sergent Coupler
Insert the friction spring (I only included this picture as I was surprised the camera got the shot through the magnifying lens!)
Ready to be closed up
Reinstall the coupler box lid and trucks (if needed) Note to be sure to only tighten the coupler lid so much, the coupler needs to be able to swing.
In the end, you can have your TrueLine Trains cars and Sergents too! Here's the slab sided hopper, with a Trueline Caboose - note that nice and tight coupler distance!