Truck mount verses Body mount. So you guys are saying it is better to have truck mounted couplers on shorter (old vintage) passenger cars when running on radius smaller than 20-22"?
I have some old vintage cars that are all truck mounted and occasionally they will uncouple going up and incline and sometimes they appear to be pulled off the track when rounding an 18" radius elevated section?
To be clear, I'm advising the use of truck-mounted couplers on every piece of rolling stock, locomotives, freight cars, and passenger cars, of any vintage, if you have sharp curves (18"-22" radius for HO) (9-3/4"-12" radius for N)
The reason for truck-mounts on tight curves is that the couplers tend to stay over the center of the track when they go through a curve. Body-mounted couplers are more realistic, since that's where prototype cars have their couplers mounted. Body-mounts also have an advantage when backing a train into a siding or yard track. The pushing action from the locomotive, is transmitted back through the train by the car frames, not the trucks. This helps keep the cars in line with one another, and decreases the chance of pushing a car up and off the rails.
Truck-mounted couplers, during an identical backing move, pass all the pushing motion through the trucks. Trucks are designed to swivel around the kingpin that holds the truck to the car frame. Pushing on something that swivels is somewhat like trying to push a chain up a hill. The things you're pushing are flexible, and don't want to stay straight when pushed.
So why not just use body mounts on every layout, no matter what the curves are? Because, if you look down between two cars equipped with body-mounted couplers as they go through a tight curve, you'll see that the couplers are not in the center of the track, but way off to the outside of the curve. The longer the car, the more overhang. The greater overhang just pushes the couplers further out toward the outside of the curve. That's bad when pulling the cars, and far worse when pushing the same string of cars. When pulling a train, most of the locomotive's pulling force is pulling the train forward. However, some of that same pulling force is also trying to drag the outside wheels up and off the outside rail. When the train is being pushed backward, a lot of the pushing force is trying to do the same thing, but remember the earlier chain analogy. Pull hard on a chain and what do you get? A straight chain, every link in line with all the others. Push on the same chain and what do you get? An instantly, very crooked, chain, with the links every which way.
Think of an aerial view of a train wreck. The cars are pushed right, left, & all over the place. A moving train packs a whole lot of pushing force!
Finally we come to the worst case scenario for coupler mounting. If you have body-mounted couplers on a locomotive, and truck-mounted couplers on the car directly behind the locomotive, derailments are very likely, as your train passes through a tight curve. That body-mount on the loco is pushing sideways toward the outside of the curve. It easily pushes the truck-mounted coupler on the following car sideways too. Meanwhile the truck-mounted coupler is responding to this outward push by doing it's own thing, swiveling the truck it's mounted to, right into the outside rail, and often the wheel will climb right up and over the rail!
This is why I emphasized pick ONE mounting system for all the couplers on all your rolling stock. If you have tight curves, use truck-mounts. If you have broad curves, use body mounts.
Traction Fan :smilie_daumenpos: