Repairing Marx one-way couplers

Last Updated on April 23, 2017 by Dave Farquhar

Marx one-way couplers were an effort to provide trains that could automatically couple and uncouple. The design was exceptionally reliable, as long as the trains were carefully stored after use. It’s not uncommon today to find them in inoperable condition, but it’s possible to repair them.

Prior to World War II, every train manufacturer tried different ways to make trains that could automatically couple and uncouple, with varying degrees of success. None were particularly realistic, and Marx’s design was probably the ugliest, but did I mention it worked really well?

The one-way coupler design consists of a post on one end of the car and a pincher mechanism on the other end. The pincher grabs onto the post, and can only be released by pulling a lever on the underside of the car. But the pincher coupler consisted of three pressed steel parts, two parts formed of wire, a spring, and two rivets–an uncharacteristically complex design for the cost-conscious Marx. Marx made them from 1936 to 1941, but didn’t reintroduce it after World War II, replacing it with the tilt-type coupler it introduced with its scale cars in 1941-42. The tilt coupler wasn’t very realistic either, but it was far simpler.

When properly assembled, the wires in the one-way couplers resemble a squared-off “J” and they engage slots in the pinchers. I sometimes find them outside of the slots. To replace them, gently bend the upper leg of the “J” slightly so that it more closely resembles an “L,” then slide it up into the slot, then gently form it back into the shape of the squared-off “J.”

Marx one-way coupler
This coupler, although rusty, functions well. Note the placement of the pinchers, spring, levers and wires. When the spring is missing, the pinchers are often spun out of place. The spring is the easiest part to lose, but fortunately it’s also the cheapest and easiest to replace.

The couplers frequently are also missing the spring. A well-stocked hardware store may have a suitable small spring. The closest match I could find locally was Hillman #71, which costs about 85 cents. Cutting one in half worked, and allowed me to repair a coupler on two cars. See the photo for the correct placement; it’s much easier to see from the photo than to describe.

My local supply of Hillman #71 dried up, but I found another alternative. Century Spring #C-51 also works when cut to length. If you can’t find either part number locally, look for a 1/8-inch spring that you can cut to a length of about 11 millimeters or 7/16 inch.

It’s also possible for the couplers to rust enough to seize themselves into an inoperable position. If that happens, applying a bit of Evaporust or Rail-Zip to them and letting them sit for around 30 minutes usually frees them up.

If the post is missing, it may be possible to rig something up to replace it, but Robert Grossman sells a replacement post for $2. It’s his part number 204.

Since these cars were only made for about five years and were more expensive than the 4-wheel variety, they are harder to find today but not impossible. The easiest way to find them, or parts for them, is to search Ebay for Marx one-way coupler or 8-wheel Marx. Either way you’ll have to sort through some plastic and 3/16 scale and non-train items, but by covering both bases, you can find some gems or bargains others won’t notice.

If you’re interested in Marx, here’s a summary of other types of Marx couplers.

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