ScaleTrains Trinity 31K Crude Oil Tank Car Coupler Conversions

The standard metal shelf type couplers on these units both look good and function well, but I wanted the ability to use magnetic uncouplers during operations. I decided to make the conversion to Kadee #158 couplers, a drop in non-shelf type semi-scale whisker coupler.


Until Kadee or ScaleTrains creates a scale operating shelf type coupler I figure function is well worth the small tradeoff in realism. A common problem with coupler conversions is height, and these cars were no exception. Luckily, I was able to shim without affecting the tracking of these cars using the method detailed below.


Kadee #158 sits several millimeters too low on the stock setup

My first thought was to contact ScaleTrains and was quickly sent additional shims, but later I realized more shims wouldn’t fix the problem. Because of the amount of adjustment necessary, adding a stack of shims pushes the top of the truck bolster lower than the centering pin, imparting a fair amount of side play in the truck. This also happened when testing the conventional Kadee fiber shims which did not produce satisfactory results.


The addition of shims will cause the truck to sit below the mount pin and lose center

After some measuring and web searching, I decided I would extend the truck pin with washers and sandwich the truck in a new mount below the original mounting location. Luckily, had everything I needed. I also felt the original mounting screws were too short and I had stripped one during trials, so I ordered #0 machine screws to replace them.


The new hardware, see below for order details

I didn’t have an exact plan when I ordered, but was confident I’d be able to figure out something. I ordered machine screws though the originals are course threaded, and they fit perfectly. I ordered both 1/4″ and 5/16″ lengths. After the order arrived, some quick trial and error yielded an elegant solution. The following picture shows the buildup on the screw. Note the truck perfectly sits around the narrower washers.


1/4″ screw, wide flange #0 washer, two standard #0 washers, and another wide flange to sandwich the truck bolster and preserve centering


The assembly less the top washer now offers plenty of mounting height flexibility


The truck replaced, now NMRA compliant

While shimming the trucks, I noticed this buildup of washers raised the car body to the perfect height. I had one car that was too high, but, by omitting the top washer and using a larger shim as shown below, was able to achieve the correct height. Only one car required a 5/16″ screw due to stripped threads.


This setup works perfectly if only minimal shimming is required


Averaged less than 10 minutes per car to swap couplers and adjust heights, 8 cars at a time


Order from

Overall this small project was far more successful than I had anticipated. The ScaleTrains trucks use dimensions that made finding exact-fit washers much easier than expected. Not only does this fix the coupler heights, but it maintains zero slop in the trucks and allows for a wide adjustment range. Note, some of the couplers do droop in the coupler pockets, and a common way to fix this is styrene sheet shims placed in the coupler box itself. I wasn’t too concerned about the droop in the couplers as it didn’t prevent correct coupler operation after shimming. Another benefit of the retrofit is that the truck bolster is isolated between washers which means that the screw can be tightened and still allow for very smooth rotation. A few hours of work and my fleet was converted and is now better than new for less than $0.50 per car!

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