Passenger car diaphragms

Today, a big box of passenger car diaphragms arrived in the mail from “S”cenery Unlimited* and, since I was in the mood, I immediately got to work installing them on some passenger cars.

The diaphragms are quite nice. They consist of a flexible rubber bellows, fitted with steel plates inside, and a brass striker plate on the end.

Some quick dry-fitting made me realize I would have to modify the stock diaphragms. For one thing, the brass striker plate includes interlocking tabs that connect adjacent cars. It also includes etched “Made in Korea” and “Scenery Unlimited” markings. Obviously, these are intended for passenger trains that run as units, without switching. On my layout, the exposed ends of the passenger cars would look odd with tabs and writing. Also, on my layout, the 42″ radius curves are a little tight for full, working diaphragms.

Once I decided how I would modify the parts, the work went quickly. I had four cars fitted in about two hours.

I started by determining that I would use the brass striker plate as the mounting plate for the car. That would require removing the two tabs designed to interlock with an adjacent diaphragm. I clipped these shorter with a side-cutter, then carefully filed away the remaining material:

Passenger car diaphragms
(Stock diaphragm on the left. Modified diaphragm on the right)

Each diaphragm has a bellows with three folds. They were too deep for my purposes, and I determined that I would have to remove one of the folds. I carefully sliced the rubber between two of the aluminum plates with a sharp knife to remove the fold farthest from the brass plate, then trimmed the rubber with a pair of scissors:

Passenger car diaphragms
(Stock diaphragm at left. Sliced diaphragm at right. Remove the aluminum plate from the sliced-away rubber and save it)

I repurposed the aluminum plate from inside the third fold as my new striker plate. I blackened the edges of the plate with a permanent marker. I noticed that one side of the plate has sharp edges, while the side is smooth. I glued the plate to the thinner diaphragm with CA, so that the smoother side is facing outward:

Passenger car diaphragms
(Stock diaphragm on the left. Modified diaphragm on the right, ready to install on a car)

I glued the diaphragm to the end of a car with CA, positioning the brass plate adjacent to the car end. At this point, I realized that despite removing one third of the thickness of the diaphragm, it still projected beyond the coupler. This, I knew, would cause no end of problems:

Passenger car diaphragms
(Asking for trouble)

Since I already modify all of my couplers, the fix was pretty straightforward. Normally, as part of my coupler tuning procedure, I replace the spring in the draft gear with a piece of styrene, as shown here:

Passenger car diaphragms
(Standard installation)

This prevents the coupler from sliding in and out of the pocket, thus minimizing the slack action. (There’s still a bit of slack, but it’s all in the coupler knuckles – not in the shanks.) I realized I could solve my diaphragm clearance problem by moving the styrene spacer to the other side of the draft gear post, as shown here:

Passenger car diaphragms
(Extended shank installation)

The coupler works the same as it did before, but it now enjoys a longer shank – and it now projects sufficiently to solve my diaphragm clearance problem:

Passenger car diaphragms
(All clear!)

In addition to preventing the diaphragms from pushing passenger cars off the rails on my curves, I’ll also be able to get a manual uncoupling tool into position between a passenger car and a freight car or locomotive.

In operation, adjacent diaphragms don’t quite touch. This photo shows two cars equipped with modified diaphragms, and with the slack stretched:

Passenger car diaphragms
(Mind the gap…)

I can live with that gap. It’s certainly better than the space between cars before the diaphragms were added. In addition, my mixed trains only had one passenger-carrying car on them, and I’m not sure the diaphragms would even have been hooked up between the combine and adjacent express car during normal operation on the line to Port Rowan.

I’ve now done the four passenger cars that I regularly run in mixed train service, and I bought extra diaphragms for future projects.

I think they look rather striking…

(*Check the “Links” section on this blog’s home page for the most up-to-date links)

15 thoughts on “Diaphragms

  1. Passenger cars used longer couplers than freight cars, so your approach is quite prototypical. I don’t know of long-shank couplers in S, so this is a good workaround.

    • Hi Steve:
      There’s only one S scale Kadee – well, two of you count colour choice (brown or black).
      Very good point!

  2. It should be possible, in theory at least, to split the plastic tube and put pieces either side of the mounting pillar, to get the diaphragms close but not quite touching.

    Out of curiosity, did you try running the coaches with the closer spacing, and the rubbing plates pressed against each other? I ask as I wondered if your transition curves might help ease any problems. (I have a similar minimum radius to you, so have a keen interest in knowing!)


    • Hi Simon:
      I did not do the tests you suggest. In addition to concerns about my minimum radius, I wanted easy (or easier) access to the couplers – and that would require cutting back the diaphragms.
      Keep in mind that what I’ve built is really a switching layout. At the end of a run in Port Rowan, the “passenger/express/LCL” portion of the mixed train is switched out of the consist and reordered – for example, the LCL boxcar is moved to the opposite end of the passenger equipment. Doing this switching with full-depth diaphragms would be problematic, if not impossible.
      Finally, I’m pretty sure the mixed train operated with the diaphragms in their “stowed” position. They had no reason to walk between the cars so they may not have bothered deploying them. Regardless, the diaphragms would be stowed on the opposite ends, where the two cars are not adjacent (which are what you see most on the layout anyway).
      If I’d built a layout with long consists of passenger carrying equipment that didn’t get regularly switched, I might have done things differently. But I think it’s appropriate to tailor equipment to the layout one is building…

    • And yes, I’ve thought of splitting the styrene piece inside the draft gear box to adjust the length of the coupler shank. Nice to see someone else thinking along those lines too… 🙂

  3. Being the picky type, I just have to comment on the too-clean look of the aluminum striker plate. A bit of rust, dust, brownish coloring and rubbing marks would make it look more like the photos I have seen in various books. It might become less striking, but more realistic. Just a thought…..not a criticism. Ed L.

    • Hi Ed:
      It’s a good one and I’ve had that thought myself. I have not yet weathered my recently completed baggage car and plan to do the striker plates on all of my passenger cars when I do.
      Rome wasn’t built, etc…

  4. Trevor, I do hope that “S”cenery has found a better source for his diaphragms. I purchased a pair many years ago as the older MPH were discontinued. Since I really didn’t need them I stashed them away, but came across them a few years back. The back rubber had rotted leaving only the frames and bits of rubber, while a couple of packages of the MPH survived just fine. I hope your beautiful work is not in vain.

    • Hi Bob:
      Thanks for the information.
      Since posting this, I’ve had several people mention this problem with the “S”cenery Unlimited diaphragms. Naturally, I already had them in stock so I’ve gone ahead and used them. If the worst happens, I’ll replace them with something else – perhaps the scratch-built-from-paper diaphragms suggested by South Wind Models and written about by Dick Karnes in the S Scale SIG’s Journal.
      Or, maybe I’ll get lucky. We’ll see…

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