Lionel trains have had many coupler designs over the years. I have a Lionel Dockside Switcher that had the rear coupler replaced. When running, any little bump would cause the rear coupler to uncouple.
After thorough checking, I found the coupler spring had no tension when the coupler was closed on the rear coupler. It barely had any tension to resist the movement of the un-coupler device. The front coupler is shorter and the equivalent spring on the front was compressed and held tension at all times in the shorter coupler assembly. It did not have problems. The spring on the rear needed to be a longer spring to keep proper tension on the coupling mechanism when closed.
The coupler was not designed to be disassembled. What I did was use my fingernail to compress part of the spring and then use a flat-bladed screwdriver tip to stretch a spring. coil I did this in 3 spots on the spring. Now there is tension on the spring, even in the closed state. The coupler no longer opens when there is any bump or drastic speed change. It still works as it should when an un-coupler track is used.
Last Update Dec 29, 2021