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Peter's Model Railroading | Articles | Rolling Stock Details | Couplers
Sergent Couplers (new)


This is the Sergent Engineering "Magnetic Uncoupling Wand". This is needed to raise the magnetic ball inside the coupler so that the coupler face is free to move, to open, and therefore allow uncoupling. It works like a charm.

In December 2013 Frank Sergent announced that the new S-scale coupler would be available soon. Design issues delayed the release until May 2014. However, in June of that year, Frank announced that he had discovered a production problem with the S-scale couplers, and the coupler would not be available again until April 2015. I was able to get a set of the "May 2014" version of the couplers, which I will cover here.

Please note that shortly after Frank released this final redesigned version, he retired and stopped selling these couplers. He made the design publicly available to anyone who wants to produce these, but so far no one has. So, this page, too, is offered for historical purposes.

The coupler doesn't come with a draft gear box, but the Kadee ones for S-scale fit perfectly. Alternatively, Smoky Mountain Model Works produces a new draft gear box for S-scale that was designed for the Sergent coupler, supports self-centering, and has a narrower box. This photo shows what is inside one package, i.e. the parts to make four individual couplers, or enough for two cars/engines. The largest parts (left-middle) are the main coupler bodies. The coupler heads (center-bottom) go into the body, and the cover (right-middle) holds the coupler head in place. The plastic bag contains the metal balls and springs.

Each package contains five springs and five balls (only four are shown in this photo). So, you get one extra of each. Remember, Frank strongly urges us to not touch the metal balls with our fingers, because the oils on our skin could start interfering with the ball's workings later on.

Really the only thing that these "May" versions of the couplers require you to do is to file off the sprue remains from the coupler head. The one on the left is as-is, while the one on the right shows the head filed smooth. It is my understanding that the later ones didn't require this. If you have done any kind of model building, doing this filing work is not a big deal.

Frank recommends painting before assembly, but I plan to hand-paint mine (my rolling stock inventory is quite small), and I plan to paint them matching the body color of the car or engine into which they will be installed, so there will be a variety of colors. Anyway, assembly of the coupler is actually simple. Take your time with the first one, but after that it will go quite quickly. Put the main coupler body upside-down, such that the cup, into which the ball fits, is up. Pick up the ball with a pair of small tweezers and place it in the cup.

Then take a look at the coupler head (the small part on the right in the photo above). A few of mine seem to have some tan-colored material in their sockets for the pins (I later on found out that Sergent tumbles the parts in a crushed-walnut hulls mixture to remove flash). I used the point of the tweezers to work that material out. Then the head can be placed on top of the pin of the coupler body. As shown in the photo, make sure the head is near its "closed" position.

You can then place the cover part on top, which holds the coupler head in place. Note the pins on it, both by the coupler head and on the other end by the main body part. That is how it falls in place.

Before applying glue, verify that the coupler head can be moved. As you see here, I didn't pay attention to the coupler head when I placed the cover on it, so it has moved too far open, and so the coupler head won't move. A simple check to verify that the coupler head indeed moves keeps you from making this mistake. I caught it before I applied the glue.

This shows the coupler head in its "closed" position.

The orange lines point to where the superglue is supposed to be applied. I used a pin to apply a tiny amount of the glue at those spots. I then let it set for 30 minutes, and then I could pick it up and test the head. Note that the coupler is actually in its upside-down position here, so you can freely move the coupler head. Don't flip the coupler right-side up yet, until you are absolutely sure the glue has completely cured, or else the ball could become glued internally.

The Sergent couplers do not come with a draft gear box, but the Kadee S/On3 ones are a perfect fit. The center pin of the box perfectly fits the hole in the coupler body.

The spring provided with the coupler is to be inserted as shown in the photo. This provides a slight bit of resistance to keep the coupler from swinging left or right. That is what makes it possible to position the coupler (left, right, or center), and then back up the engine to the train to get it to couple, just like in the prototype. Without the spring, the coupler can easily move out of position due to the vibration of the engine. Opinion: other brands of couplers (regardless of scale) have automatic centering springs. This is fine, but it makes it near impossible to couple cars/engines on curved track. The Sergent couplers allow you to position the couplers the way you want to them to mate, and then move the engine to make the connection. For me that is a very important feature.

The coupler's shank also perfectly clears the opening of the Kadee draft gear box. The coupler moves freely without resistance, and there is no flop.

And this is what it is all about: a coupler that looks just like the prototype, and is sized correctly for the scale. Obviously I need to do some painting and touch-ups here and there, but you get the idea.

Here's another view.

This photo shows one of the Walthers Proto MAX couplers installed on the tank car on the left, while the Sergent S-scale coupler is installed on the flat car on the right. As you can see, the coupler heads' sizes are almost identical. But the reason why I took this photo was to show that you can still run a train with mixed couplers. When I touch the Sergent magnetic wand to the Sergent coupler, the coupler opens. This allows the tank car to uncouple, without having to touch its coupler at all. When I then want to couple back up, the face of the tank car's coupler presses against the back of the Sergent coupler, which causes it to close. So, operations using these two mixed couplers should work, perhaps even better than before. I do not have any of the Kadee couplers or the S-Helper Service couplers installed on my equipment, so I cannot do a similar test with them. I suspect that since they are quite a bit larger, it won't work well, if at all, with those couplers.

Here's an overhead view of the two different types of couplers.

Two cars converted to the Sergent couplers. Don't they just look great?! And so real!

A nice shot of how the couplers connect.

Instead of painting the couplers, I decided to just apply the rust colored Bragdon Enterprises weathering powder shown in the photo. I really liked the result, as shown with the coupler on the right. The weathering powder does not negatively impacts the functioning of the coupler head itself.

I have converted eight cars and my main switching engine to using Sergent couplers, and I have done a few mini operating sessions by myself. Here are my thoughts so far.

Using the Kadee boxes, they are relatively easy to install, because most S-scale cars, especially ready-to-run ones, come set-up for them. For kit cars you have to do some extra work.

The couplers stay nice and straight while the train is moving, whether the cars are being pulled or pushed. Uncoupling goes very well. It is easy to uncouple a car and then push it into a siding where normal uncoupling would be difficult to do due to scenery or reach.

It is with coupling the cars that I have some problems. It seems that lighter cars do not put enough stress on the couplers to make them fully close. From the Sergent Yahoo! discussion group, it seems that some in the HO-scale community are having the same problems. For me, this is especially true for my styrene flat cars. Those weigh about half the NMRA recommended weight. Placing a temporary load on them (e.g. a nearby automobile) seems to resolve the problem. My box cars, which are heavier, seem to have no problems.

I have also started to file down the surfaces within the coupler where they move against each other. I did not do that with the flat car couplers (which were the first ones I did). I tried putting graphite powder in the flat car couplers, as per Sergent's instructions, but that seems to make no difference. The later ones I did (the box cars), I have not applied any graphite to the couplers at all, and they work fine.

The flat car couplers I covered with Bragdon weathering powders. I have concluded that that seems to have no negative impact on the workings of the coupler (note that not all of my flat cars are causing me problems; just one, and the front coupler of my NW2 switcher, which has not been weathered yet). So, my conclusion so far is that filing down the moving surfaces of the parts in the coupler during construction is a good idea, and weathering them once assembled seems to not have an impact on them.

The only other thing I have found that is annoying is the simulated uncoupling lever of the S-Helper Service NW2 engine. It is made out of a metal that draws the Sergent magnet rod to it, always making me having to fight it to be able to uncouple the coupler.

Doing switching operations, which is all I do on my layout, now takes significantly more time. You have to stop and line up the couplers before coupling. If they don't couple, you have to keep trying. However, that is exactly what they have to do in the real world, so it makes operations more realistic.

As an aside, the other thing I found is that the magnet rod works fine with turning on and off my battery-powered engines. So, other than needing pushbuttons to control my turnouts, all I need is that magnet rod to run my entire layout!

After installation, some of my couplers aren't quite even with the ones of the next car/engine. I can fix that with shims, but, I found the linked-to video (below) clearly shows there is a coupler height difference between a car and an engine, so that is quite prototypical.
(external link: Prototype Coupling of Cars)