Whereas passenger cars do not derail when being pulled forward by one or more locos, they are prone to derailment in reverse when being pushed by one or more locos. My question is, why?
Rich
What type of passenger cars are you talking about?
The Rivarossi/AHM/Athearn derail more in reverse because the couplers are truck mounted rather than body mounted. Pushing binds the trucks against opposite sides of the rails and consequently pushes the wheel flanges up and over the rail tops.
Some other brands have coupler “swing pads” where the coupler is body mouted but will move from side to side. This can mean that when pushing the couplers swing and the cars are not being pushed straight backwards but “sideways” down the track grinding the trucks into one rail or the other. Once again more derailments.
Finally just straight body mounted coupler cars should not be any more prone to derailment than other freight cars of similar length other then perhaps flat cars because a flat car has a lower center of gravity. Long cars derail more on curves when being pushed because they don’t follow the curve as well as a smaller car so once again they are being pushed sideways not straight down the rail. That is also why long cars derail more easily than short when being pulled as they are being pulled a bit sideways. The sharper the curve the more pronounced the overswing to the outside and more sideways they get pulled.
Rich,
I have Athearn BB heavyweights and streamliners. I also have the Con-Cor streamliners. All are the short 72 foot versions with truck mount couplers. I can back up through double switches, or around 18" curves and they never derail. So I have not seen that issue.
Once when I replaced some wheels on freight cars with P2K wheelsets, I began to have derailments only in reverse. What I found out was the point to point axle length was too short. When backing up, the axles were dropping down in the trucks on the inboard side of the curve and would derail.
Mostly Walthers 85’ passenger cars.
Rich
Have you checked each truck to make certain they are on “square” to the bolster, they both pivot easily, and that one (and only one) has a slight rock to it? I have found that many of the Walthers cars seem to have the screw that holds the truck on put in at a slight angle.
One cause of passenger car reverse move derailments is a stiff diaphram. If they rub each other when backing up, one striker plate can get locked up with another in a curve or through a switch and off comes the car. Going forward, the slack in the couplers allows for less tension on the diaphram if they even touch at all.
Paul A. Cutler III
On the Walthers Heavyweights that I have, it’s a combo of the stiff diaphragms and the trucks making contact with parts of the frame or screwheads.
It is virtually never a problem, shoved or towed, on curves broader than 29" with my particular items.
-Crandell
Ditto Crandell. I go down to 27" no issues. 24" diaphram related occasional derail. below 24 it just all breaks loose.
so in theory the only way to prevent this on ones Model railroad is to place a back in station at an angle perpendicular to the main right?
literally all of my N scale passenger cars save for two MTL’s have truck mounted couplers, so it’s a challenge for the most part. I’m thinking that in order to avoid derailments, I must remove some what considered normal station entry design practices from possible back in station designs, and passenger car/ freight car stub ended storage yards.
all of my primary passenger units: 2 E5’s, 1 E7, 1 F3A, 2 E8A’s, and a lone GS4 have truck mount couplers on the rear truck/tender truck respectively (minus the E8’s which are those goofy Con Cor/rivarossi’s with moving pilots)
only body mounted units I plan on purchasing that will serve as protection or stand in power will be 5 GP9’s eventually…
I have switch enough passenger cars at one club I was a member of for years to know there shouldn’t be any issues backing passenger cars even with truck mounted couplers.
I suspect there’s several things at play here and one may be high speed reverse moves
Gary,The answer to your question is no…There’s no reason to place your station on a angle…
N Scale passenger cars like freight cars can be switch so,the real issue is speed in reverse moves.
Once modelers learn not to turn the throttle knob to the extreme right they will learn reverse moves are indeed derailment free regardless if the couplers are truck mounted or body mounted.
Thanks, guys, for all of your replies. I am going to study a little more what you all had to say and try to observe more closely what happens to make those cars derail in reverse.
What I still find perplexing, though, is why it never happens in the forward direction, but derailments do occur occasionally in reverse, never on straight sections of track, not over straight sections of turnouts but sometimes on the divergent section of turnouts, and most often on curves. I will concede that it is most likely to happen at higher, than at lower, speeds.
My thinking is that it has something to do with the heavier weight of the locos being pushed up against the lighter weight of the passenger cars.
I should mention that my track is Code 83, my turnouts are all #6, and my curved sections of track are mostly 32" radius or broader with an occasional 30" radius but never tighter.
Any more thoughts on these potential issues?
Rich
Rich,If that was the case I would be in deep kimchi because all of my cars are factory weight and my engines are heavier.
Care for a wild shot in the dark? Check your truck swing your truck screws may be a hair to tight.
Recheck your wheel gauge…They will go out of gauge.The how or why they work their selves out of gauge I know not.
My leave I take.
Larry, you raise two very good issues.
Regarding the truck screws being too tight, I agree that it can be a problem, a big problem. But, I have taken care to make sure that the screws are not too tight. If the cars don’t derail in forward, then they shouldn’t derail in reverse, at least as it relates to the free movement of the trucks.
As far as wheels being out of gauge, I have to say that for all of my passenger cars, I have yet to find a wheelset out of gauge.
I am not trying to be argumentative, and I appreciate your advice. I just haven’t been able to identify my problem yet. Derailments in reverse have become few and far between, but they still do occur on occasion.
Rich
Rich,No problems…Like I said I was taking a wild shot in the dark…[(-D]
Whatever the issue is it has to be simple and a easy fix.I’ve see that problem before and I just can’t remember…
Sheesh growing old and becoming a tad forgetful about hobby things is getting to be a royal pain.
There’s really a pretty simple visual inspection to see what is going on, pulling and pushing. Take two Kadee couplers, hold by the shank in one hand and by the shank in the other hand, couple them together and pull with both hands, you will see that the couplers grab at the very tip,where the little flange is, hard to uncouple. Now do the same thing, but push them together and see how wide the gap gets, the harder you push, if on a curve at all one coupler will only be pushing the other center part to the side, causing it to derail. Doesn’t get an easier to see than that.
Frank
Frank,If that was the case you couldn’t switch cars because you couldn’t back up since the same would happen with freight cars.
There is absolutely no reason why passenger cars can be backed…I switched the passenger terminal at one club for years with zero issues.
Gotta be a very simple problem we’re overlooking.
Larry,
I am not disputing anyone’s reasoning behind what is going on, only giving an example of what is actually happening and the same holds true for freight cars. The heavier the weight of the push is, which includes speed, the more the coupler will spread. Do the simple visual test and see. On a prototype, the couplers do not spread open, the slack is compressed. You yourself should know, can you pull a coupler pin, when it is under tension?
Frank
Backing any kind of car is alway more prone to derailments than pulling forward. Backing, the force of the locomotive goes into the couplers. Part of the force is straight back, and part is sideways. Things are never perfect, there is always some sidethrust. The couplers are spring mounted, and the sidethrust makes them buckle farther to the side. As the coupler buckles sideways, the side force gets stronger too. Whereas pulling forward, the side force is less, and tends to pull the couplers into line, rather than pushing them out of line.
Truck mounted couplers aggravate the problem. The coupler thrust goes right to the trucks, twists them sideways, and then a flange climbs over the rail head and the car is on the ground. On the other hand you need truck mounted couplers to operate long cars on the tight curves that most of us have. Long in HO is 70
Rich
The cars being pulled allow some small distance between the diaphrams, but when you back up, the diaphrams tend to rub and this can cause a derailment on a turnout. This is only one possibility and there are probably other factors involved.
CZ