Couplers-Body Mount vs. Truck Mount

Model Railroader General Discussion (Model Railroader)
1

[soapbox] I was laid up for awhile and had the opportunity to review a lot of my MRM Dream Plan Build series DVD’s. I came across several that stressed the fact that body mounted couplers out-perform truck mounted couplers on curves, staying coupled better, but they never specifically said why, nor if were a specific guage ( I run HO). Can anyone answer this question? It would seem to me that a good truck mounted coupler would work better because not only would the truck turn on a curve, the coupler would also have extra “give” thus less automatic uncoupling. But experience shows me this is not necessarily so. Since I do not have a geometry or engineering background so I am having a hard time understanding this dilemma. Any help would be appreciated.

Thanks[banghead]

2

Truck mounted couplers seem to be better at negotiating tight radius curves as long as you’re only going forward, but place all of the pressure on the wheel flanges and can push the wheels off of the track when attempting to back up.

Body mounted couplers can cause problems on tight radius curves because of the amount of overswing at the ends of the rolling stock, particularly long passenger cars where the wheels are quite a distance from the end; but body mounted couplers are better for backing around a tight radius because the pressure is on the end of the car and not the wheels.

For optimum performance, body mounted couplers and large radius curves seem to be the best combination.

Hope this helps answer your questions.

3

Short answer is that when couplers are attached to the trucks the couplers tend to act like a lever on the trucks. When the car is on a curve the coupler forces are no longer in line with the center pin of the truck, so it tends to try to rotate the truck, which can affect the tracking of the truck, which can derail the car. When the couplers are body mounted the coupler forces go through the car and the trucks are free to track independently of the coupler forces.

Dave H.

4

Also the real thing uses body mounts, which might give you a clue.

Bob

5

Truck-mounted couplers (often inaccurately called “Talgo” couplers) work as well as body-mount couplers, generally, when pulling a train. And in many cases, they work even better (e.g.: the Athearn streamlined passenger cars) on curves, when pulling a train. The passenger cars, however, may have an advantage due to the longer wheelbase of the trucks concerned.

However, when pushing cars, particularly cars with the short-wheelbase freight trucks, as in setting out cars when switching or working in a yard, a very different situation arises. Mind you, it’s not quite as bad with knuckle couplers as it is with the old horn-hook couplers, but it’s still problematic. Pushing cars, the forces on the couplers will twist the truck to the side as it enters a curve (“curve” includes the diverging route of a turnout), causing the flanges to “pick” any irregularity in the rail (track joints, switch frogs, etc.) and derail. The horn-hook couplers exacerbate the problem by adding a sideways force of their own due to their springing arrangement.

The problem is even present on straight track while pushing cars, for the same reasons. Because the pushing force is transferred to the body of the car through the truck mounting, the trucks will try to swivel as the inertia is being overcome, again forcing the flanges against the side of the rail.

An even more difficult situation arises when a car with body-mount couplers is coupled to a car with truck-mount couplers. The body-mount couplers swing out more in a sharp curve, which can rip the car with the truck-mount couplers right off the track.

There will be folks, I’m sure, who will claim that they can back long strings of cars with truck-mounted couplers through all kinds of complex trackwork. However, they are the exception rather than the rule. I suspect they have unusually good trackwork.

In sum, I would agree with the conventional w

6

Body mount couplers keep the train on the track while backing up. In a backing move, the truck mount couplers tend to twist the trucks a little bit sideways, and then a flange climbs over the railhead and the train is on the ground.

A lot of passenger cars come with truck mount couplers in the hope that they will ease the car around sharp curves. I converted a batch of 80 foot IHC cars to body mount #5 (short shank) couplers and I can get the resulting train around an 18" curve.

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[quote user=“gmcrail”]

Truck-mounted couplers (often inaccurately called “Talgo” couplers) work as well as body-mount couplers, generally, when pulling a train. And in many cases, they work even better (e.g.: the Athearn streamlined passenger cars) on curves, when pulling a train. The passenger cars, however, may have an advantage due to the longer wheelbase of the trucks concerned.

However, when pushing cars, particularly cars with the short-wheelbase freight trucks, as in setting out cars when switching or working in a yard, a very different situation arises. Mind you, it’s not quite as bad with knuckle couplers as it is with the old horn-hook couplers, but it’s still problematic. Pushing cars, the forces on the couplers will twist the truck to the side as it enters a curve (“curve” includes the diverging route of a turnout), causing the flanges to “pick” any irregularity in the rail (track joints, switch frogs, etc.) and derail. The horn-hook couplers exacerbate the problem by adding a sideways force of their own due to their springing arrangement.

The problem is even present on straight track while pushing cars, for the same reasons. Because the pushing force is transferred to the body of the car through the truck mounting, the trucks will try to swivel as the inertia is being overcome, again forcing the flanges against the side of the rail.

An even more difficult situation arises when a car with body-mount couplers is coupled to a car with truck-mount couplers. The body-mount couplers swing out more in a sharp curve, which can rip the car with the truck-mount couplers right off the track.

There will be folks, I’m sure, who will claim that they can back long strings of cars with truck-mounted couplers through all kinds of complex trackwork. However, they are the exception rather than the rule. I suspect they have unusually good trackwork.

In sum, I would agree

8

Suffice it to say this is a very hot topic in N Scale…Both camps has made excellent points but,and IHMO the next major advancement in N will be body mounted couplers.

Why the dilemma in N? Both methods of coupler mounts works quite well but,many fear the body mounts will not work on the tight 9 3/4 curves but,I believe they will if one follows the HO 18" curve rule.

As far as truck mounts in HO…Except for long wheel base cars why bother with truck mounts?

9

I think the ‘talgo’ term came from a European source. The ideal arrangement would be to have the coupler drawbar pivot at the truck center, but not with the truck. This would transmit the pulling/pushing forces to the bolster king pin.

I actual practice, a good body mount coupler will get most freight cars around 22" radius curves. I have had no problems with long auto racks and passenger cars on the 33" radius at the club. My home layout has 22" radius curves and I usually run 40-50’ freight cars and 60’ passenger cars with no problems.

Jim Bernier

10

I stand with a foot in each camp - all of my passenger stock and my longer freight cars have body mounted couplers. The shorter freight cars (the majority) have truck-mounted couplers. The joker is that the ‘trucks’ are what the Rev. Awdry would have defined as ‘troublesome,’ four wheel cars with fairly long wheelbases, journal boxes mounted in fixed pedestals.

IMHO, the real trick to getting long cars around tight radii lies in the trackwork - namely, proper spiral easements. If the diaphragms on your passenger cars stay lined up, so will the couplers. If the coupled ends of two cars have a serious offset when one is on tangent track and the other is on curved track there WILL be side pressure on couplers and wheel flanges. Add in that sectional track has a rail joint right there…

There is one down side to having really long ‘bogie stock’ coupled to my 4-wheelers. There is a serious offset between the two when both cars are on a tight curve. On certain routings through the netherworld I have to be careful to put an intermediate-length car between the container flat and the 15-ton box vans. The good news is that those are routes where the container flat will have little or no reason to go.

Chuck (modeling Central Japan in September, 1964)

11

Thanks guys!

You have helped me solve a problem I have been looking at for awhile.

TheK4Kid

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The term Talgo refers to a train called the Talgo train, which was first developed in the late-Fifties era. The cars are designed to lean into (tilt) curves by tilting the car bodies to counteract centrifugal forces. This allows the train to take curves at higher speeds. The Talgo train currently operates only in Spain. I suspect that the trucks and couplers are mounted independently of the tilting body. The Talgo train has a bunch of wild and freaky features, like variable wheel gauge, which I’ve only just come to realize…

Model railroad manufacturers picked up on the idea, but changed it to mount the couplers rigidly on the truck frame. These came about, BTW, about the time sprung trucks fell out of use because manufacturers found it to be cheaper to mold the truck bolster, sideframes, and coupler mount as one piece. (And I totally disagree with that trend, in almost all ways! It may be cheaper, but it made trackwork much more critical.)

And yes, the NMRA is incorrect in that reference, but they are using a common term for that particular arrangement, which should technically be called “truck-mounted couplers”, or - even pickier - “rigidly truck-mounted couplers”, when referring to the couplers, or when referring to the trucks, “trucks with…” . It’s a lot easier to say “Talgo trucks”, or Talgo couplers. And everyone who’s a model railroader (almost) knows what you’re talking about. Nobody outside the hobby will have a clue, of course.[:D]

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[soapbox] Thanks for the input, it helped alot. My biggest problem has been my Walthers 85’ passenger cars which seem to me to be somekind of of a combination of body mount and truck mount. And it’s always in the curves that they come apart. I have super elevated the outside rail, increased the radius from 22" to 25" and still loose the consist on the curve (and usually in the tunnels-why make it easy?) I think maybe I’ll try installing a couple of #5’s and boxes and see what happens.[:)]

Larry

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Here a Talgo, there a talgo…

Hey guys, its not unusual for a word to have different, and even disparate, meanings. “Talgo” (spelled with a lower-case “t”) is a commonly accepted term in reference to truck-mounted coupler on a model train, and in my book, is an acceptable definition in that context.

The only general English dictionary definition I’ve found is for “Talgo”, meaning a Spanish manufacturer of railway vehicles, as well as an ancronym for Tren Articulado Ligero Goicoechea Oriol, a high-speed articulated train of Spanish invention for intercity passenger operations .

Regardless, “talgo couplers” meaning truck-mounted couplers has been in common use in the hobby for many, many decades.

Mark

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Ooops… NMRA spells “Talgo” always with a capital “T”. My mistake.

Mark

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gmcrail,
The Talgo was developed in Spain during the 1940’s, not the late 1950’s. The tilting carbody generally is just for passenger comfort. The tilt allows for greater speeds because passengers are pressed downward, rather than sideways. The same applies for the Acela with it’s active tilting mechanism. Talgo trains are currently operated in the Pacific Northwest by Amtrak.

Model railroad manufacturers were putting the couplers on the trucks rather than on the bodies for many years before Talgo got off the ground. Lionel, for example, used them and so did American Flyer on their pre-WWII toy trains.

Sprung trucks aren’t that good unless they are correctly sprung. Most, if not all, sprung trucks are too tight or are too stiff to actually work. If the weight of the car isn’t enough to cause the springs to deflect, then you might as well have a solid truck. When sprung trucks hit a track bump, they may deflect upwards, but then they don’t settle back down. This means a truck is now going down the track on 2 or 3 wheels, which leads to derailments.

Paul A. Cutler III

Weather Or No Go New Haven

17

I know this is going OT, but…

As a young model railroader, I thought that sprung trucks were the end all, be all of trucks. I soon found out, as noted above, that unless the trucks are “loose”, they are more problems than rigid trucks. I find that the Kadee trucks are really nice, and pretty much function as they should. On the other hand, I purchased a Challenger Imports boxcar a couple of years back that had sprung trucks that were useless at best. They were really stiff and seemed to serve no function. They may have worked well if I added 5 pounds of lead to the car.

I really like the sprung trucks that come on brass passenger cars from importers such as TCY. They are really neat until you

18

If you have grades and mid-train or helper locos, then truck-mount couplers are even more problematic. It is very easy for a helper set to derail the car(s) in front of it because the compression forces are higher when pushing the train up the grade.

In N scale the problem is also more acute because (a) most cars are pretty light and (b) most cars have truck mount couplers while most locos have body-mount couplers.

Adding weight and/or using oversized “pizza cutter” wheels are not good solutions, because the helpers only have to push all that much harder on grades to overcome the additional weight and/or drag. Oversized wheels also are not NMRA compliant and only work on oversized rail.

N scale modelers also sometimes add “drag springs” to their cars to help overcome the “pogo” problem that happens with spring-loaded couplers. The additional drag from these springs can compound the above truck-mount coupler problems.

Truck-mount couplers also require additional clearance in order to operate properly. This is why most N-scale cars sit about a scale foot or so higher above the rails than their repective prototype – the so-called “high rider” effect. Oversized wheels also add to this effect. If you notice, marketing photos of new N-scale cars are nearly always taken from a high angle in order to minimize the look of this.

19

Well, it depends on what kind of coupler you’re using. If you’re using tension-lock couplers (also known as hook and loop couplers), bogie(I use Brit terminology) mounted works better. I’ve backed two coaches with bogie-mounted tension lock couplers around an 18" radius curve at high speed with no trouble. Knuckle couplers, I don’t know for myself. I stopped using them, except for on a pair of partially-anglicised Athearn flatbeds.

20

Walthers uses a swinging mount for the coupler pocket which allows greater coupler side movement to take tight curves. I found the trouble is with the wheels hitting the center sill and/or the truck sideframe screws rubbing on the body contact strip or the dummy body bolster cast on the floor.

Turn the car upside down and grind away whatever is interfering with free truck movement. Try adding a very thin #10 washer between truck and car floor and a spacer between kingpin bolt and the boss it screws into so the truck won’t be clamped immovable by the washer.

These modifications will let the Walthers cars track well in tight curves but I find the plastic spring ears on the swinging coupler pocket mount often fatigue and don’t center the couplers for reliable coupling. For reliable coupling I recommend removing Walters coupler mount and replacing it with a Kade #454 Swing Bracket.

While you have the trucks off the car, you might as well tune the them. Disassemble them, check the wheel gauge and correct it if necessary. Check the sideframe journal bearings with a reaming tool. Carefully hone the axle tips with a very fine file or crocus cloth glued to a popsickle stick. Hone, don’t round the tip. When finished, you should not feel a burr when the tip is pulled acrosss your finger tip. Add the tinest speck of oil to each axle tip as you reassemble the truck. A drop is far too much.

You’ll be suprised how much better the trucks roll!