Installing "scale" couplers to replace the large AF compatible couplers which come with SHS rolling stock is one of the easiest modifications you can make, and makes a major difference in scale appearance. Replacing the couplers on original American Flyer or Lionel manufactured American Flyer is not easy, however, and requires modification of the car. This is not what is being discussed here. I'm only talking about SHS cars and locos, although most of what I say will also apply to American Models, S Scale America and similar cars. The purpose of this document is to explore some of the trade-offs between the two types of couplers. For the purpose of this discussion, "scale" couplers mean Kadee 802/808 or SHS 01295 couplers. The opinions expressed are those of the author (Bill Clark) and don't necessarily represent reality. I am certainly open to comment and criticism, however, and will be happy to include other views if you send them to me! AF compatible couplers have the following advantages:
1. Looks. If you like the looks of AF couplers and they fit the ambiance of your AF layout, then you probably should stick with them. If the AF couplers look too big for your comfort, or you like your cars coupled more closely, you might want to change.
By the way, you can go to "scale" couplers without going to "scale" code 110 wheels, and many do. I personally use code 125 track, AF compatible (Hi-rail) wheels, and "scale" couplers.
Also by the way, SHS offers a 01310 AF compatible coupler to allow closer coupling of freight cars while keeping the AF compatible coupler.
2. Operation. The "scale" couplers (Kadee 802/808 and SHS 01295) lend themselves very well to a "switching" type of operation. AF compatible work very well with tight turns, s-curves, and changes in track elevation.
I operate on a friend's layout most weeks. His layout is designed for full operation with switch lists, train orders, switching yards and industries. Six people operate at once, with 4 mainline engineers picking up and dropping cars at industries, a yardmaster/helper engineer, and dispatcher. We use "scale" couplers.
There are magnets under the track at the beginning of most sidings. When the coupler passes over the magnet, tension on the coupler (pulling or pushing) keeps it from uncoupling. To uncouple, you stop with the couplers over the magnet, back up just enough to remove tension, then pull away. The magnet pulls each coupler to the opposite side, and opens the jaws. The couplers stay to the side while over the magnet, so if you now back the uncoupled couplers together, they will be in a "delayed uncouple" state, which means you can push the uncoupled cars without them re coupling. This is very handy for "spotting" cars at industries. This is much less complicated than it sounds. We also use an HO sized Rix magnetic uncoupler or a small pointed "swizzle stick" for uncoupling where there are no magnets.
There are two main reasons why the AF compatible couplers work so well on tight curves or elevation changes. First, the coupler faces are much larger so that the alignment of the couplers is not so critical. Secondly, the standard mounting for the AF compatible coupler is pivoted from the truck bolster, while the standard "scale" coupler is mounted to the car body. Mounting the coupler to the car body is much more likely to pull the car off the track on sharp turns or S curves, especially long cars.I don't have exact numbers, but my experience is that any of the SHS freight cars or locos with body-mounted "scale" couplers can make it around 20" curves, and through s curves created by using 2 AF switches to connect parallel tracks, without a problem. I use AF compatible (Hi-rail) wheels, by the way. Passenger cars are too long, and will be pulled off the track. To avoid that, I used a Talgo (truck) mount by cutting the AF coupler off its shank and gluing an 802 coupler box in its place. That way the coupler can turn with the truck, and the car can negotiate the same corners as with the AF compatible coupler. Automatic coupling and decoupling were compromised, however.
Another potential compromise is to use "scale" couplers on the freight cars, and leave passenger trains with AF compatible couplers. A third option is the bolster mounted dummy (not operating) scale couplers supplied by American Models for the passenger cars.
So I don't think there is a right or wrong answer that applies to everyone. There will always be tradeoffs and compromises. If I have missed something, or made a mistake, or you can suggest an improvement to this essay, please let me know!
Part 2: Which "scale" coupler should I use?