Installing Truck-Mount TN Couplers

オロネ25-901 (with body-mount TN coupler) and オハネ25-100 (with truck-mount TN coupler)

Not every Tomix or Micro Ace train accepts the fancy-pants body-mount TN couplers. Sometimes you have to make do with compromises. Which is what Tomix’s truck-mount TN couplers are: A compromise. They work, but they’re not nearly as cool, and don’t look quite as good. And they’re harder to install. But, in the end, I think they are still worthwhile to bother with. Here’s how to install them.

Remove the truck by unscrewing it. Watch those springs!

This time, I’m installing couplers into my Tomix “Yumekuukan” set. Although Tomix recommends truck-mount TN couplers for every car, the three “Yumekuukan” cars at the end are actually set up for body-mounts. But the token regular 24-25 sleeping cars do need truck-mounts. Begin by removing the shell in the usual manner, and then removing the screw that holds the truck in place. The reason to remove the shell is that the screw also holds the various layers of the frame in place, and you will find that you have made a mess of things if you don’t remove the shell first (this is, yes, experience speaking). Watch the springs that Tomix uses to collect current from the trucks for interior lighting: They are not affixed to anything. Set them and the screw aside.

Carefully pry the metal retaining plate from the coupler pocket. The spring inside is even more fiddly than the others.

Immediately, we are confronted with the trickiest step. You have to pry the metal retaining plate off of the coupler pocket. It is help firmly in place by tabs on the opposite side that you have to prod and poke and push with fine-tipped tweezers until the plate comes off. Don’t worry too much if you bend the plate, it is easily restored to the proper shape. Watch for the spring on the inside! Toss the Rapido coupler into your bits box, and keep the remainder somewhere handy.

A sprue of TN couplers. Notice they two halves.

Truck-mount TN couplers have to be assembled. They come in two parts, on a sprue. Cut off the smaller of the two parts (on the bottom in the photo); it will be attached at only one point. The other half is attached at two points. Press fit the smaller part to the larger part while the larger is still on the sprue. The fitting will require some force, so make sure that the two pins are aligned precisely with the two holes. Use tweezers to make sure both halves are pressed firmly together. Cut the larger half from the sprue.

The assembled TN coupler ready for installation. Remember the right-hand rule.

The assembled coupler must be inserted right-side up, and unlike, say, Micro-Trains couplers which have a clear right-side up, these do not. It’s easy to forget which way they should go. Just remember the right-hand rule: When properly installed, and the car is on the track, the coupler should resemble your right hand reaching out for a handshake. Except, of course, the coupler pocket is on the bottom of the truck, so when you’re installing it, it will look like your left hand extended. So maybe I should call it the left-hand rule?

Insert the spring into the pocket first, then the coupler.

Insert the spring into the coupler pocket. It will need to be compressed ever so slightly, and this is the step where a spring is most likely to go flying, so take great care. Once the spring is in place, press the nub on the end of the coupler into the spring to secure the spring, then slip the end of the coupler into the pocket, compressing the spring even more. This too is a little tricky, as once again the spring may go flying off. But once it’s in place, the assembly is fairly stable.

Press the retaining plate back over the pocket.

Finally, carefully press the retaining plate back over the pocket, making sure the two metal tabs are properly seated on the opposite side. Then reattach the truck to the frame with the screw. Once both trucks are complete, you can put the shell back on. Make sure that all the arrows on the shell and frame are pointing in the same direction.

For the curious, I measured the various coupling distances on this set. Between cars with truck-mounted Rapido couplers, the gap between carriages is 6.3mm. When these are swapped for truck-mount TNs, the gap is reduced to about 5.3mm. The gap between a carriage with a truck-mount TN coupler and a carriage with a body-mount TN coupler is even less at 4.0mm.