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Monday, March 26, 2012

Replacing snap-in trucks

Many older models from such sources as AHM, LifeLike, Model Power and others might have car bodies which were attractive starting points for a needed model, but were delivered with snap-in trucks, usually with “Talgo” couplers of the horn-hook variety, looking like this:

These trucks largely had terrible wheelsets, poorly rendered side frames (the one shown above is better than average), and an unacceptable coupler arrangement.
     When starting on an upgrade project for one of these cars, I have tried (in the distant past) cutting off the coupler mounting and salvaging the sideframes to re-use the snap-in feature, but this results in sloppy truck location, and ultimately just retains a disappointing feature of these models. Nowadays trucks like this go straight into the trash. Only exception would be if I want to harvest the journal box covers to replace poorer ones on other trucks. In a couple of cases, I have harvested them, saved the covers in my “Trucks” parts drawer, then discarded the remains.
     The way to fix the truck attachment is to fill the large bolster holes in the underframe, so that they can be drilled and tapped for your favorite truck screw (mine is 2-56). Then the correct coupler pad height needs to be checked, which I do by mounting the trucks and then comparing the height of the bottom of the car floor to the Kadee coupler height gauge (this height check is shown later in this post). If necessary, I then cut down or shim this location so that Kadee coupler boxes can be installed flat on the floor (normally with a 2-56 screw).
     My favorite approach to filling that large hole in the bolster is as follows. I use Evergreen styrene 1/8-inch tubing, which is a little undersize, and shim it with 0.010 or 0.015-inch styrene sheet to fill the bolster hole. If the hole is larger still, I like Plastruct 4-mm styrene rod. I sometimes back this hole filler with a piece of styrene sheet on the inside of the floor, such as 0.060-inch thick, to ensure plenty of material for screws to thread into. I usually use Plastruct’s “Plastic Weld” cement for this job, as it really does weld the plastic parts together. Once dry, the tubing or rod can then be drilled all the way through, and tapped for 2-56 screws.
     Here are two examples (models in progress for future posts).

This is a LifeLike one-piece reefer body. The bolster hole was filled with the 1/8-inch tubing, shimmed as needed to fill the hole, and then backfilled with modeling putty. The coupler pad shown is at about the right height but needed to be corrected (more on this in a moment).
     Below is an AHM underbody, with both a large bolster hole for the snap-in trucks and a second large hole, which was created in molding the attachment for the car weight.

I filled the bolster hole with the tubing, and then a backing piece was added inside the car above the coupler pad, to ensure enough thread grip. Here are the corrected bolster holes, already tapped 2-56:

The backing pieces above the coupler location can be seen through the end-most holes.
     I’m always surprised how many modelers who use the Kadee coupler height gauge don’t realize that the top of the back end of the same gauge is the height of a car floor correctly situated for installation of a Kadee coupler box. Shown below is the indication for one of the LifeLike reefer bodies, riding on its future trucks. It’s worth mentioning that the bolster height can vary from one model truck manufacturer to another, so this measurement needs to be done with the car’s intended trucks.

You can just see that the coupler pad cast onto the body needs to be removed to about the level of the floor. My typical modeling process would be to remove most of that coupler pad and re-check to be sure of the necessary height.
     With the coupler pad all but removed, and trucks and couplers in place, the coupler height can be checked again with the Kadee gauge, as you see here, and it looks like it is right at the desired height. The car body (lettering mostly stripped) is ready for detailing.

     Well, those are my techniques for replacing snap-in trucks and for installing the Kadee couplers on those car bodies. I have some upcoming posts which take advantage of these procedures in preparing a model.
Tony Thompson


  1. I have Mantua Cars with snap on trucks. I want to change them to Kadee Trucks and couplings. How do I know what number unit to buy???
    Thanks for the Great Information.

    1. I can't see how to answer because I don't know what kind of trucks you intend to use. Do you mean the Kadee "talgo" trucks? I hope not, because I think body mounting the couplers is far better. If you fill the truck hole, as I showed in the post, you can then attach Kadee or any trucks with a conventional screw -- I use 2-56.
      Tony Thompson