I have experienced problems with PW couplers of the design shown below failing to consistently uncouple on my uncoupler track. The coupler shown below is on a "one-piece" plastic AAR truck on my 243W tender before spring installation:
Without disassembling the uncoupler mechanism, you can "thread" a conical collector roller spring onto the disc shaft as shown below:
It takes some "doing" and you must ensure that you thread the spring so the small end is up. The spring prevents the disc from sticking in the "up" position while allowing enough "play" in the shaft for free downward motion during uncoupling. You may have to hold the "uncouple" button down a couple of seconds but the coupler will open consistently, even at track voltage as low as 9V:
I hope this helps folks with the same problem I had.
