Trying to troubleshoot weak electrocoupler

Since it still opens when unplugged it is probably the spring. Some have reported that they have been able to open the knuckle with a pair of pliers but I have never been successful that way. I usually need to remove and replace the rivet that holds the movable part of the knuckle in. It is very easy to do if you have a replacement for the rivet. If you are careful you may even be able to reuse the original rivet. In any case there is a small coil spring (looks like a ball point pen spring) inside the coupler. The idea is to stretch the original spring so that it is about 3/4 to 1 inch long.

Al

You can open an electrocoupler very easily with nothing more than a paperclip.  Bend it straight and just press it in to the coupler body, the coupler pops open.

That is fine John but that won't get at the latch spring. It is the latch spring that is week and needs to be strengthened. The only way I know to get at it is to remove the knuckle.

Al

If you actually have to get to the spring, you're obviously correct.   FWIW, if I have to open it up, I'd replace the spring with a new one, my experience with stretching springs is spotty, and the "fix" doesn't often last that long.

The coil coupler on your DD-35 is most likely fine. The coupler is failing mechanically as a result of it not being parallel with the center rail. The pressure applied to the back of the knuckle is allowing it to fail (and subsequently pop open). You can literally unplug the coupler (from the truck) and the problem will recur, showing the mechnical failure. Simply snug up the screw that mounts the coupler to the truck frame and the probglem should disappear (don't forget to plug it back in!).

If anyone has a coupler where it is very stiff once the coupler knuckle opens I advise you blow a puff of dry graphite lubricant into the center hole where the slug resides (while the coupler is closed and locked). Then fire the coupler a few times (yes, you will see a "puff" of smoke exit the coupler throat for a few activations). You will also notice the knuckle pivots much easier and prevents you from having to "smash" the coupler into the reciprocating coupler to get it to close.